Subject: Re: Making Vars outer-join aware

From: Tom Lane <[email-masked]>
Date: Mon, 23 Jan 2023 15:38:06 -0500

The cfbot shows that this needs to be rebased over 8eba3e3f0.
(Just code motion, no interesting changes.)

Richard, are you planning to review this any more?  I'm getting
a little antsy to get it committed.  For such a large patch,
it's surprising it's had so few conflicts to date.

			regards, tom lane

commit a02e22407fc3215896efe7b6e5063ba272ca02ee
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:09:39 2023 -0500

    Add overview documentation.

diff --git a/src/backend/optimizer/README b/src/backend/optimizer/README
index 41c120e0cd..191ad4c457 100644
--- a/src/backend/optimizer/README
+++ b/src/backend/optimizer/README
@@ -295,6 +295,239 @@ Therefore, we don't merge FROM-lists if the result would have too many
 FROM-items in one list.

+Vars and PlaceHolderVars
+------------------------
+
+A Var node is simply the parse-tree representation of a table column
+reference.  However, in the presence of outer joins, that concept is
+more subtle than it might seem.  We need to distinguish the values of
+a Var "above" and "below" any outer join that could force the Var to
+null.  As an example, consider
+
+	SELECT * FROM t1 LEFT JOIN t2 ON (t1.x = t2.y) WHERE foo(t2.z)
+
+(Assume foo() is not strict, so that we can't reduce the left join to
+a plain join.)  A naive implementation might try to push the foo(t2.z)
+call down to the scan of t2, but that is not correct because
+(a) what foo() should actually see for a null-extended join row is NULL,
+and (b) if foo() returns false, we should suppress the t1 row from the
+join altogether, not emit it with a null-extended t2 row.  On the other
+hand, it *would* be correct (and desirable) to push that call down to
+the scan level if the query were
+
+	SELECT * FROM t1 LEFT JOIN t2 ON (t1.x = t2.y AND foo(t2.z))
+
+This motivates considering "t2.z" within the left join's ON clause
+to be a different value from "t2.z" outside the JOIN clause.  The
+former can be identified with t2.z as seen at the relation scan level,
+but the latter can't.
+
+Another example occurs in connection with EquivalenceClasses (discussed
+below).  Given
+
+	SELECT * FROM t1 LEFT JOIN t2 ON (t1.x = t2.y) WHERE t1.x = 42
+
+we would like to use the EquivalenceClass mechanisms to derive "t2.y = 42"
+to use as a restriction clause for the scan of t2.  (That works, because t2
+rows having y different from 42 cannot affect the query result.)  However,
+it'd be wrong to conclude that t2.y will be equal to t1.x in every joined
+row.  Part of the solution to this problem is to deem that "t2.y" in the
+ON clause refers to the relation-scan-level value of t2.y, but not to the
+value that y will have in joined rows, where it might be NULL rather than
+equal to t1.x.
+
+Therefore, Var nodes are decorated with "varnullingrels", which are sets
+of the rangetable indexes of outer joins that potentially null the Var
+at the point where it appears in the query.  (Using a set, not an ordered
+list, is fine since it doesn't matter which join forced the value to null;
+and that avoids having to change the representation when we consider
+different outer-join orders.)  In the examples above, all occurrences of
+t1.x would have empty varnullingrels, since the left join doesn't null t1.
+The t2 references within the JOIN ON clauses would also have empty
+varnullingrels.  But outside the JOIN clauses, any Vars referencing t2
+would have varnullingrels containing the index of the JOIN's rangetable
+entry (RTE), so that they'd be understood as potentially different from
+the t2 values seen at scan level.  Labeling t2.z in the WHERE clause with
+the JOIN's RT index lets us recognize that that occurrence of foo(t2.z)
+cannot be pushed down to the t2 scan level: we cannot evaluate that value
+at the scan level, but only after the join has been done.
+
+For LEFT and RIGHT outer joins, only Vars coming from the nullable side
+of the join are marked with that join's RT index.  For FULL joins, Vars
+from both inputs are marked.  (Such marking doesn't let us tell which
+side of the full join a Var came from; but that information can be found
+elsewhere at need.)
+
+Notionally, a Var having nonempty varnullingrels can be thought of as
+	CASE WHEN any-of-these-outer-joins-produced-a-null-extended-row
+	  THEN NULL
+	  ELSE the-scan-level-value-of-the-column
+	  END
+It's only notional, because no such calculation is ever done explicitly.
+In a finished plan, Vars occurring in scan-level plan nodes represent
+the actual table column values, but upper-level Vars are always
+references to outputs of lower-level plan nodes.  When a join node emits
+a null-extended row, it just returns nulls for the relevant output
+columns rather than copying up values from its input.  Because we don't
+ever have to do this calculation explicitly, it's not necessary to
+distinguish which side of an outer join got null-extended, which'd
+otherwise be essential information for FULL JOIN cases.
+
+Outer join identity 3 (discussed above) complicates this picture
+a bit.  In the form
+	A leftjoin (B leftjoin C on (Pbc)) on (Pab)
+all of the Vars in clauses Pbc and Pab will have empty varnullingrels,
+but if we start with
+	(A leftjoin B on (Pab)) leftjoin C on (Pbc)
+then the parser will have marked Pbc's B Vars with the A/B join's
+RT index, making this form artificially different from the first.
+For discussion's sake, let's denote this marking with a star:
+	(A leftjoin B on (Pab)) leftjoin C on (Pb*c)
+To cope with this, once we have detected that commuting these joins
+is legal, we generate both the Pbc and Pb*c forms of that ON clause,
+by either removing or adding the first join's RT index in the B Vars
+that the parser created.  While generating paths for a plan step that
+joins B and C, we include as a relevant join qual only the form that
+is appropriate depending on whether A has already been joined to B.
+
+It's also worth noting that identity 3 makes "the left join's RT index"
+itself a bit of a fuzzy concept, since the syntactic scope of each join
+RTE will depend on which form was produced by the parser.  We resolve
+this by considering that a left join's identity is determined by its
+minimum set of right-hand-side input relations.  In both forms allowed
+by identity 3, we can identify the first join as having minimum RHS B
+and the second join as having minimum RHS C.
+
+Another thing to notice is that C Vars appearing outside the nested
+JOIN clauses will be marked as nulled by both left joins if the
+original parser input was in the first form of identity 3, but if the
+parser input was in the second form, such Vars will only be marked as
+nulled by the second join.  This is not really a semantic problem:
+such Vars will be marked the same way throughout the upper part of the
+query, so they will all look equal() which is correct; and they will not
+look equal() to any C Var appearing in the JOIN ON clause or below these
+joins.  However, when building Vars representing the outputs of join
+relations, we need to ensure that their varnullingrels are set to
+values consistent with the syntactic join order, so that they will
+appear equal() to pre-existing Vars in the upper part of the query.
+
+Outer joins also complicate handling of subquery pull-up.  Consider
+
+	SELECT ..., ss.x FROM tab1
+	  LEFT JOIN (SELECT *, 42 AS x FROM tab2) ss ON ...
+
+We want to be able to pull up the subquery as discussed previously,
+but we can't just replace the "ss.x" Var in the top-level SELECT list
+with the constant 42.  That'd result in always emitting 42, rather
+than emitting NULL in null-extended join rows.
+
+To solve this, we introduce the concept of PlaceHolderVars.
+A PlaceHolderVar is somewhat like a Var, in that its value originates
+at a relation scan level and can then be forced to null by higher-level
+outer joins; hence PlaceHolderVars carry a set of nulling rel IDs just
+like Vars.  Unlike a Var, whose original value comes from a table,
+a PlaceHolderVar's original value is defined by a query-determined
+expression ("42" in this example); so we represent the PlaceHolderVar
+as a node with that expression as child.  We insert a PlaceHolderVar
+whenever subquery pullup needs to replace a subquery-referencing Var
+that has nonempty varnullingrels with an expression that is not simply a
+Var.  (When the replacement expression is a pulled-up Var, we can just
+add the replaced Var's varnullingrels to its set.  Also, if the replaced
+Var has empty varnullingrels, we don't need a PlaceHolderVar: there is
+nothing that'd force the value to null, so the pulled-up expression is
+fine to use as-is.)  In a finished plan, a PlaceHolderVar becomes just
+the contained expression at whatever plan level it's supposed to be
+evaluated at, and then upper-level occurrences are replaced by Var
+references to that output column of the lower plan level.  That causes
+the value to go to null when appropriate at an outer join, in the same
+way as for normal Vars.  Thus, PlaceHolderVars are never seen outside
+the planner.
+
+PlaceHolderVars (PHVs) are more complicated than Vars in another way:
+their original value might need to be calculated at a join, not a
+base-level relation scan.  This can happen when a pulled-up subquery
+contains a join.  Because of this, a PHV can create a join order
+constraint that wouldn't otherwise exist, to ensure that it can
+be calculated before it is used.  A PHV's expression can also contain
+LATERAL references, adding complications that are discussed below.
+
+
+Relation Identification and Qual Clause Placement
+-------------------------------------------------
+
+A qual clause obtained from WHERE or JOIN/ON can be enforced at the lowest
+scan or join level that includes all relations used in the clause.  For
+this purpose we consider that outer joins listed in varnullingrels or
+phnullingrels are used in the clause, since we can't compute the qual's
+result correctly until we know whether such Vars have gone to null.
+
+The one exception to this general rule is that a non-degenerate outer
+JOIN/ON qual (one that references the non-nullable side of the join)
+cannot be enforced below that join, even if it doesn't reference the
+nullable side.  Pushing it down into the non-nullable side would result
+in rows disappearing from the join's result, rather than appearing as
+null-extended rows.  To handle that, when we identify such a qual we
+artificially add the join's minimum input relid set to the set of
+relations it is considered to use, forcing it to be evaluated exactly at
+that join level.  The same happens for outer-join quals that mention no
+relations at all.
+
+When attaching a qual clause to a join plan node that is performing an
+outer join, the qual clause is considered a "join clause" (that is, it is
+applied before the join performs null-extension) if it does not reference
+that outer join in any varnullingrels or phnullingrels set, or a "filter
+clause" (applied after null-extension) if it does reference that outer
+join.  A qual clause that originally appeared in that outer join's JOIN/ON
+will fall into the first category, since the parser would not have marked
+any of its Vars as referencing the outer join.  A qual clause that
+originally came from some upper ON clause or WHERE clause will be seen as
+referencing the outer join if it references any of the nullable side's
+Vars, since those Vars will be so marked by the parser.  But, if such a
+qual does not reference any nullable-side Vars, it's okay to push it down
+into the non-nullable side, so it won't get attached to the join node in
+the first place.
+
+These things lead us to identify join relations within the planner
+by the sets of base relation RT indexes plus outer join RT indexes
+that they include.  In that way, the sets of relations used by qual
+clauses can be directly compared to join relations' relid sets to
+see where to place the clauses.  These identifying sets are unique
+because, for any given collection of base relations, there is only
+one valid set of outer joins to have performed along the way to
+joining that set of base relations (although the order of applying
+them could vary, as discussed above).
+
+SEMI joins do not have RT indexes, because they are artifacts made by
+the planner rather than the parser.  (We could create rangetable
+entries for them, but there seems no need at present.)  This does not
+cause a problem for qual placement, because the nullable side of a
+semijoin is not referenceable from above the join, so there is never a
+need to cite it in varnullingrels or phnullingrels.  It does not cause a
+problem for join relation identification either, since whether a semijoin
+has been completed is again implicit in the set of base relations
+included in the join.
+
+There is one additional complication for qual clause placement, which
+occurs when we have made multiple versions of an outer-join clause as
+described previously (that is, we have both "Pbc" and "Pb*c" forms of
+the same clause seen in outer join identity 3).  When forming an outer
+join we only want to apply one of the redundant versions of the clause.
+If we are forming the B/C join without having yet computed the A/B
+join, it's easy to reject the "Pb*c" form since its required relid
+set includes the A/B join relid which is not in the input.  However,
+if we form B/C after A/B, then both forms of the clause are applicable
+so far as that test can tell.  We have to look more closely to notice
+that the "Pbc" clause form refers to relation B which is no longer
+directly accessible.  While this check is straightforward, it's not
+especially cheap (see clause_is_computable_at()).  To avoid doing it
+unnecessarily, we mark the variant versions of a redundant clause as
+either "has_clone" or "is_clone".  When considering a clone clause,
+we must check clause_is_computable_at() to disentangle which version
+to apply at the current join level.  (In debug builds, we also Assert
+that non-clone clauses are validly computable at the current level;
+but that seems too expensive for production usage.)
+
+
 Optimizer Functions
 -------------------
 
@@ -437,11 +670,10 @@ inputs.
 EquivalenceClasses
 ------------------
 
-During the deconstruct_jointree() scan of the query's qual clauses, we look
-for mergejoinable equality clauses A = B whose applicability is not delayed
-by an outer join; these are called "equivalence clauses".  When we find
-one, we create an EquivalenceClass containing the expressions A and B to
-record this knowledge.  If we later find another equivalence clause B = C,
+During the deconstruct_jointree() scan of the query's qual clauses, we
+look for mergejoinable equality clauses A = B.  When we find one, we
+create an EquivalenceClass containing the expressions A and B to record
+that they are equal.  If we later find another equivalence clause B = C,
 we add C to the existing EquivalenceClass for {A B}; this may require
 merging two existing EquivalenceClasses.  At the end of the scan, we have
 sets of values that are known all transitively equal to each other.  We can
@@ -473,15 +705,89 @@ asserts that at any plan node where more than one of its member values
 can be computed, output rows in which the values are not all equal may
 be discarded without affecting the query result.  (We require all levels
 of the plan to enforce EquivalenceClasses, hence a join need not recheck
-equality of values that were computable by one of its children.)  For an
-ordinary EquivalenceClass that is "valid everywhere", we can further infer
-that the values are all non-null, because all mergejoinable operators are
-strict.  However, we also allow equivalence clauses that appear below the
-nullable side of an outer join to form EquivalenceClasses; for these
-classes, the interpretation is that either all the values are equal, or
-all (except pseudo-constants) have gone to null.  (This requires a
-limitation that non-constant members be strict, else they might not go
-to null when the other members do.)  Consider for example
+equality of values that were computable by one of its children.)
+
+Outer joins complicate this picture quite a bit, however.  While we could
+theoretically use mergejoinable equality clauses that appear in outer-join
+conditions as sources of EquivalenceClasses, there's a serious difficulty:
+the resulting deductions are not valid everywhere.  For example, given
+
+	SELECT * FROM a LEFT JOIN b ON (a.x = b.y AND a.x = 42);
+
+we can safely derive b.y = 42 and use that in the scan of B, because B
+rows not having b.y = 42 will not contribute to the join result.  However,
+we cannot apply a.x = 42 at the scan of A, or we will remove rows that
+should appear in the join result.  We could apply a.x = 42 as an outer join
+condition (and then it would be unnecessary to also check a.x = b.y).
+This is not yet implemented, however.
+
+A related issue is that constants appearing below an outer join are
+less constant than they appear.  Ordinarily, if we find "A = 1" and
+"B = 1", it's okay to put A and B into the same EquivalenceClass.
+But consider
+
+	SELECT * FROM a
+	  LEFT JOIN (SELECT * FROM b WHERE b.z = 1) ss ON (a.x = b.y)
+	WHERE a.x = 1;
+
+It would be a serious error to conclude that a.x = b.z, so we cannot
+form a single EquivalenceClass {a.x b.z 1}.
+
+This leads to considering EquivalenceClasses as applying within "join
+domains", which are sets of relations that are inner-joined to each other.
+(We can treat semijoins as if they were inner joins for this purpose.)
+There is a top-level join domain, and then each outer join in the query
+creates a new join domain comprising its nullable side.  Full joins create
+two join domains, one for each side.  EquivalenceClasses generated from
+WHERE are associated with the top-level join domain.  EquivalenceClasses
+generated from the ON clause of an outer join are associated with the
+domain created by that outer join.  EquivalenceClasses generated from the
+ON clause of an inner or semi join are associated with the syntactically
+most closely nested join domain.
+
+Having defined these domains, we can fix the not-so-constant-constants
+problem by considering that constants only match EquivalenceClass members
+when they come from clauses within the same join domain.  In the above
+example, this means we keep {a.x 1} and {b.z 1} as separate
+EquivalenceClasses and don't erroneously merge them.  We don't have to
+worry about this for Vars (or expressions containing Vars), because
+references to the "same" column from different join domains will have
+different varnullingrels and thus won't be equal() anyway.
+
+In the future, the join-domain concept may allow us to treat mergejoinable
+outer-join conditions as sources of EquivalenceClasses.  The idea would be
+that conditions derived from such classes could only be enforced at scans
+or joins that are within the appropriate join domain.  This is not
+implemented yet, however, as the details are trickier than they appear.
+
+Another instructive example is:
+
+	SELECT *
+	  FROM a LEFT JOIN
+	       (SELECT * FROM b JOIN c ON b.y = c.z WHERE b.y = 10) ss
+	       ON a.x = ss.y
+	  ORDER BY ss.y;
+
+We can form the EquivalenceClass {b.y c.z 10} and thereby apply c.z = 10
+while scanning C, as well as b.y = 10 while scanning B, so that no clause
+needs to be checked at the inner join.  The left-join clause "a.x = ss.y"
+(really "a.x = b.y") is not considered an equivalence clause, so we do
+not insert a.x into that same EquivalenceClass; if we did, we'd falsely
+conclude a.x = 10.  In the future though we might be able to do that,
+if we can keep from applying a.x = 10 at the scan of A, which in principle
+we could do by noting that the EquivalenceClass only applies within the
+{B,C} join domain.
+
+Also notice that ss.y in the ORDER BY is really b.y* (that is, the
+possibly-nulled form of b.y), so we will not confuse it with the b.y member
+of the lower EquivalenceClass.  Thus, we won't mistakenly conclude that
+that ss.y is equal to a constant, which if true would lead us to think that
+sorting for the ORDER BY is unnecessary (see discussion of PathKeys below).
+Instead, there will be a separate EquivalenceClass containing only b.y*,
+which will form the basis for the PathKey describing the required sort
+order.
+
+Also consider this variant:
 
 	SELECT *
 	  FROM a LEFT JOIN
@@ -489,27 +795,42 @@ to null when the other members do.)  Consider for example
 	       ON a.x = ss.y
 	  WHERE a.x = 42;
 
-We can form the below-outer-join EquivalenceClass {b.y c.z 10} and thereby
-apply c.z = 10 while scanning c.  (The reason we disallow outerjoin-delayed
-clauses from forming EquivalenceClasses is exactly that we want to be able
-to push any derived clauses as far down as possible.)  But once above the
-outer join it's no longer necessarily the case that b.y = 10, and thus we
-cannot use such EquivalenceClasses to conclude that sorting is unnecessary
-(see discussion of PathKeys below).
-
-In this example, notice also that a.x = ss.y (really a.x = b.y) is not an
-equivalence clause because its applicability to b is delayed by the outer
-join; thus we do not try to insert b.y into the equivalence class {a.x 42}.
-But since we see that a.x has been equated to 42 above the outer join, we
-are able to form a below-outer-join class {b.y 42}; this restriction can be
-added because no b/c row not having b.y = 42 can contribute to the result
-of the outer join, and so we need not compute such rows.  Now this class
-will get merged with {b.y c.z 10}, leading to the contradiction 10 = 42,
-which lets the planner deduce that the b/c join need not be computed at all
-because none of its rows can contribute to the outer join.  (This gets
-implemented as a gating Result filter, since more usually the potential
-contradiction involves Param values rather than just Consts, and thus has
-to be checked at runtime.)
+We still form the EquivalenceClass {b.y c.z 10}, and additionally
+we have an EquivalenceClass {a.x 42} belonging to a different join domain.
+We cannot use "a.x = b.y" to merge these classes.  However, we can compare
+that outer join clause to the existing EquivalenceClasses and form the
+derived clause "b.y = 42", which we can treat as a valid equivalence
+within the lower join domain (since no row of that domain not having
+b.y = 42 can contribute to the outer-join result).  That makes the lower
+EquivalenceClass {42 b.y c.z 10}, resulting in the contradiction 10 = 42,
+which lets the planner deduce that the B/C join need not be computed at
+all: the result of that whole join domain can be forced to empty.
+(This gets implemented as a gating Result filter, since more usually the
+potential contradiction involves Param values rather than just Consts, and
+thus it has to be checked at runtime.  We can use the join domain to
+determine the join level at which to place the gating condition.)
+
+There is an additional complication when re-ordering outer joins according
+to identity 3.  Recall that the two choices we consider for such joins are
+
+	A leftjoin (B leftjoin C on (Pbc)) on (Pab)
+	(A leftjoin B on (Pab)) leftjoin C on (Pb*c)
+
+where the star denotes varnullingrels markers on B's Vars.  When Pbc
+is (or includes) a mergejoinable clause, we have something like
+
+	A leftjoin (B leftjoin C on (b.b = c.c)) on (Pab)
+	(A leftjoin B on (Pab)) leftjoin C on (b.b* = c.c)
+
+We could generate an EquivalenceClause linking b.b and c.c, but if we
+then also try to link b.b* and c.c, we end with a nonsensical conclusion
+that b.b and b.b* are equal (at least in some parts of the plan tree).
+In any case, the conclusions we could derive from such a thing would be
+largely duplicative.  Conditions involving b.b* can't be computed below
+this join nest, while any conditions that can be computed would be
+duplicative of what we'd get from the b.b/c.c combination.  Therefore,
+we choose to generate an EquivalenceClause linking b.b and c.c, but
+"b.b* = c.c" is handled as just an ordinary clause.
 
 To aid in determining the sort ordering(s) that can work with a mergejoin,
 we mark each mergejoinable clause with the EquivalenceClasses of its left
@@ -522,7 +843,11 @@ if other equivalence clauses are later found to bear on the same
 expressions.
 
 Another way that we may form a single-item EquivalenceClass is in creation
-of a PathKey to represent a desired sort order (see below).  This is a bit
+of a PathKey to represent a desired sort order (see below).  This happens
+if an ORDER BY or GROUP BY key is not mentioned in any equivalence
+clause.  We need to reason about sort orders in such queries, and our
+representation of sort ordering is a PathKey which depends on an
+EquivalenceClass, so we have to make an EquivalenceClass.  This is a bit
 different from the above cases because such an EquivalenceClass might
 contain an aggregate function or volatile expression.  (A clause containing
 a volatile function will never be considered mergejoinable, even if its top
@@ -544,6 +869,9 @@ it's possible that it belongs to more than one.  We keep track of all the
 families to ensure that we can make use of an index belonging to any one of
 the families for mergejoin purposes.)
 
+For the same sort of reason, an EquivalenceClass is also associated
+with a particular collation, if its datatype(s) care about collation.
+
 An EquivalenceClass can contain "em_is_child" members, which are copies
 of members that contain appendrel parent relation Vars, transposed to
 contain the equivalent child-relation variables or expressions.  These
@@ -579,7 +907,7 @@ Index scans have Path.pathkeys that represent the chosen index's ordering,
 if any.  A single-key index would create a single-PathKey list, while a
 multi-column index generates a list with one element per key index column.
 Non-key columns specified in the INCLUDE clause of covering indexes don't
-have corresponding PathKeys in the list, because the have no influence on
+have corresponding PathKeys in the list, because they have no influence on
 index ordering.  (Actually, since an index can be scanned either forward or
 backward, there are two possible sort orders and two possible PathKey lists
 it can generate.)
@@ -608,9 +936,14 @@ must now be ordered too.  This is true even though we used neither an
 explicit sort nor a mergejoin on Y.  (Note: hash joins cannot be counted
 on to preserve the order of their outer relation, because the executor
 might decide to "batch" the join, so we always set pathkeys to NIL for
-a hashjoin path.)  Exception: a RIGHT or FULL join doesn't preserve the
-ordering of its outer relation, because it might insert nulls at random
-points in the ordering.
+a hashjoin path.)
+
+An outer join doesn't preserve the ordering of its nullable input
+relation(s), because it might insert nulls at random points in the
+ordering.  We don't need to think about this explicitly in the PathKey
+representation, because a PathKey representing a post-join variable
+will contain varnullingrel bits, making it not equal to a PathKey
+representing the pre-join value.
 
 In general, we can justify using EquivalenceClasses as the basis for
 pathkeys because, whenever we scan a relation containing multiple
@@ -655,14 +988,9 @@ redundancy, we save time and improve planning, since the planner will more
 easily recognize equivalent orderings as being equivalent.
 
 Another interesting property is that if the underlying EquivalenceClass
-contains a constant and is not below an outer join, then the pathkey is
-completely redundant and need not be sorted by at all!  Every row must
-contain the same constant value, so there's no need to sort.  (If the EC is
-below an outer join, we still have to sort, since some of the rows might
-have gone to null and others not.  In this case we must be careful to pick
-a non-const member to sort by.  The assumption that all the non-const
-members go to null at the same plan level is critical here, else they might
-not produce the same sort order.)  This might seem pointless because users
+contains a constant, then the pathkey is completely redundant and need not
+be sorted by at all!  Every interesting row must contain the same value,
+so there's no need to sort.  This might seem pointless because users
 are unlikely to write "... WHERE x = 42 ORDER BY x", but it allows us to
 recognize when particular index columns are irrelevant to the sort order:
 if we have "... WHERE x = 42 ORDER BY y", scanning an index on (x,y)
@@ -670,15 +998,6 @@ produces correctly ordered data without a sort step.  We used to have very
 ugly ad-hoc code to recognize that in limited contexts, but discarding
 constant ECs from pathkeys makes it happen cleanly and automatically.
 
-You might object that a below-outer-join EquivalenceClass doesn't always
-represent the same values at every level of the join tree, and so using
-it to uniquely identify a sort order is dubious.  This is true, but we
-can avoid dealing with the fact explicitly because we always consider that
-an outer join destroys any ordering of its nullable inputs.  Thus, even
-if a path was sorted by {a.x} below an outer join, we'll re-sort if that
-sort ordering was important; and so using the same PathKey for both sort
-orderings doesn't create any real problem.
-
 
 Order of processing for EquivalenceClasses and PathKeys
 -------------------------------------------------------
commit 6d24e50c60cc3d9e2a4f0c8ea58f0fdfbadf313d
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:20:40 2023 -0500

    Do assorted preliminary refactoring.
    
    This patch doesn't actually change any behavior, just lay some
    fairly boring groundwork:
    
    * Add Var.varnullingrels and PlaceHolderVar.phnullingrels fields.
    These fields are always empty as of this commit, so they don't
    affect any behavior, even though equal() will compare them.
    Update backend/nodes/ and backend/rewrite/ infrastructure as needed.
    
    * Refactor deconstruct_jointree() to split it into two passes;
    the first pass computes relid bitmapsets and the second performs
    qual distribution.  The reason for this is that when we invent
    "join domains", several patches later, we'll need to know the
    full contents of the domains before distributing quals.  It
    seems like a good idea to split up the function anyway, as it's
    gotten quite large.
    
    * Move calculation of all_baserels to deconstruct_jointree,
    because we'll soon need it to be available earlier.
    (This means that remove_rel_from_query now has to update it.)
    
    * Refactor to pass the relevant SpecialJoinInfo to
    reconsider_outer_join_clause and reconsider_full_join_clause.
    We'll need that later.
    
    * Add some rewrite functions we'll need later for adding and
    removing nullingrel bits in expression trees.
    
    Note this will require a catversion bump when committed.

diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index cad9f28ef5..fe67baf142 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -80,11 +80,13 @@ makeVar(int varno,
 	var->varlevelsup = varlevelsup;
 
 	/*
-	 * Only a few callers need to make Var nodes with varnosyn/varattnosyn
-	 * different from varno/varattno.  We don't provide separate arguments for
-	 * them, but just initialize them to the given varno/varattno.  This
-	 * reduces code clutter and chance of error for most callers.
+	 * Only a few callers need to make Var nodes with non-null varnullingrels,
+	 * or with varnosyn/varattnosyn different from varno/varattno.  We don't
+	 * provide separate arguments for them, but just initialize them to NULL
+	 * and the given varno/varattno.  This reduces code clutter and chance of
+	 * error for most callers.
 	 */
+	var->varnullingrels = NULL;
 	var->varnosyn = (Index) varno;
 	var->varattnosyn = varattno;
 
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index 8fc24c882b..dc8415a693 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -2641,6 +2641,7 @@ expression_tree_mutator_impl(Node *node,
 				Var		   *newnode;
 
 				FLATCOPY(newnode, var, Var);
+				/* Assume we need not copy the varnullingrels bitmapset */
 				return (Node *) newnode;
 			}
 			break;
@@ -3234,7 +3235,7 @@ expression_tree_mutator_impl(Node *node,
 
 				FLATCOPY(newnode, phv, PlaceHolderVar);
 				MUTATE(newnode->phexpr, phv->phexpr, Expr *);
-				/* Assume we need not copy the relids bitmapset */
+				/* Assume we need not copy the relids bitmapsets */
 				return (Node *) newnode;
 			}
 			break;
diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
index 16084842a3..8b101fc336 100644
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -383,6 +383,11 @@ JumbleExpr(JumbleState *jstate, Node *node)
 				APP_JUMB(var->varno);
 				APP_JUMB(var->varattno);
 				APP_JUMB(var->varlevelsup);
+
+				/*
+				 * We can omit varnullingrels, because it's fully determined
+				 * by varno/varlevelsup plus the Var's query location.
+				 */
 			}
 			break;
 		case T_Const:
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index c2fc568dc8..c56d3f926d 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -159,27 +159,6 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	Index		rti;
 	double		total_pages;
 
-	/*
-	 * Construct the all_baserels Relids set.
-	 */
-	root->all_baserels = NULL;
-	for (rti = 1; rti < root->simple_rel_array_size; rti++)
-	{
-		RelOptInfo *brel = root->simple_rel_array[rti];
-
-		/* there may be empty slots corresponding to non-baserel RTEs */
-		if (brel == NULL)
-			continue;
-
-		Assert(brel->relid == rti); /* sanity check on array */
-
-		/* ignore RTEs that are "other rels" */
-		if (brel->reloptkind != RELOPT_BASEREL)
-			continue;
-
-		root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
-	}
-
 	/* Mark base rels as to whether we care about fast-start plans */
 	set_base_rel_consider_startup(root);
 
@@ -207,6 +186,7 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	{
 		RelOptInfo *brel = root->simple_rel_array[rti];
 
+		/* there may be empty slots corresponding to non-baserel RTEs */
 		if (brel == NULL)
 			continue;
 
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 7d7e6facdf..783ef5aa29 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -61,10 +61,10 @@ static RestrictInfo *create_join_clause(PlannerInfo *root,
 										EquivalenceMember *rightem,
 										EquivalenceClass *parent_ec);
 static bool reconsider_outer_join_clause(PlannerInfo *root,
-										 RestrictInfo *rinfo,
+										 OuterJoinClauseInfo *ojcinfo,
 										 bool outer_on_left);
 static bool reconsider_full_join_clause(PlannerInfo *root,
-										RestrictInfo *rinfo);
+										OuterJoinClauseInfo *ojcinfo);
 static Bitmapset *get_eclass_indexes_for_relids(PlannerInfo *root,
 												Relids relids);
 static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
@@ -1977,10 +1977,12 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 		/* Process the LEFT JOIN clauses */
 		foreach(cell, root->left_join_clauses)
 		{
-			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+			OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-			if (reconsider_outer_join_clause(root, rinfo, true))
+			if (reconsider_outer_join_clause(root, ojcinfo, true))
 			{
+				RestrictInfo *rinfo = ojcinfo->rinfo;
+
 				found = true;
 				/* remove it from the list */
 				root->left_join_clauses =
@@ -1996,10 +1998,12 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 		/* Process the RIGHT JOIN clauses */
 		foreach(cell, root->right_join_clauses)
 		{
-			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+			OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-			if (reconsider_outer_join_clause(root, rinfo, false))
+			if (reconsider_outer_join_clause(root, ojcinfo, false))
 			{
+				RestrictInfo *rinfo = ojcinfo->rinfo;
+
 				found = true;
 				/* remove it from the list */
 				root->right_join_clauses =
@@ -2015,10 +2019,12 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 		/* Process the FULL JOIN clauses */
 		foreach(cell, root->full_join_clauses)
 		{
-			RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+			OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-			if (reconsider_full_join_clause(root, rinfo))
+			if (reconsider_full_join_clause(root, ojcinfo))
 			{
+				RestrictInfo *rinfo = ojcinfo->rinfo;
+
 				found = true;
 				/* remove it from the list */
 				root->full_join_clauses =
@@ -2035,21 +2041,21 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 	/* Now, any remaining clauses have to be thrown back */
 	foreach(cell, root->left_join_clauses)
 	{
-		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+		OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-		distribute_restrictinfo_to_rels(root, rinfo);
+		distribute_restrictinfo_to_rels(root, ojcinfo->rinfo);
 	}
 	foreach(cell, root->right_join_clauses)
 	{
-		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+		OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-		distribute_restrictinfo_to_rels(root, rinfo);
+		distribute_restrictinfo_to_rels(root, ojcinfo->rinfo);
 	}
 	foreach(cell, root->full_join_clauses)
 	{
-		RestrictInfo *rinfo = (RestrictInfo *) lfirst(cell);
+		OuterJoinClauseInfo *ojcinfo = (OuterJoinClauseInfo *) lfirst(cell);
 
-		distribute_restrictinfo_to_rels(root, rinfo);
+		distribute_restrictinfo_to_rels(root, ojcinfo->rinfo);
 	}
 }
 
@@ -2059,9 +2065,10 @@ reconsider_outer_join_clauses(PlannerInfo *root)
  * Returns true if we were able to propagate a constant through the clause.
  */
 static bool
-reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
+reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 							 bool outer_on_left)
 {
+	RestrictInfo *rinfo = ojcinfo->rinfo;
 	Expr	   *outervar,
 			   *innervar;
 	Oid			opno,
@@ -2185,8 +2192,9 @@ reconsider_outer_join_clause(PlannerInfo *root, RestrictInfo *rinfo,
  * Returns true if we were able to propagate a constant through the clause.
  */
 static bool
-reconsider_full_join_clause(PlannerInfo *root, RestrictInfo *rinfo)
+reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 {
+	RestrictInfo *rinfo = ojcinfo->rinfo;
 	Expr	   *leftvar;
 	Expr	   *rightvar;
 	Oid			opno,
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index d657e8f601..51b653fed4 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -349,6 +349,11 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 		}
 	}
 
+	/*
+	 * Update all_baserels and related relid sets.
+	 */
+	root->all_baserels = bms_del_member(root->all_baserels, relid);
+
 	/*
 	 * Likewise remove references from SpecialJoinInfo data structures.
 	 *
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index d60398f1c6..4acbd3df32 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -40,7 +40,40 @@ int			from_collapse_limit;
 int			join_collapse_limit;

-/* Elements of the postponed_qual_list used during deconstruct_recurse */
+/*
+ * deconstruct_jointree requires multiple passes over the join tree, because we
+ * need to finish computing JoinDomains before we start distributing quals.
+ * As long as we have to do that, other information such as the relevant
+ * qualscopes might as well be computed in the first pass too.
+ *
+ * deconstruct_recurse recursively examines the join tree and builds a List
+ * (in depth-first traversal order) of JoinTreeItem structs, which are then
+ * processed iteratively by deconstruct_distribute.
+ *
+ * The JoinTreeItem structs themselves can be freed at the end of
+ * deconstruct_jointree, but do not modify or free their substructure,
+ * as the relid sets may also be pointed to by RestrictInfo and
+ * SpecialJoinInfo nodes.
+ */
+typedef struct JoinTreeItem
+{
+	/* Fields filled during deconstruct_recurse: */
+	Node	   *jtnode;			/* jointree node to examine */
+	bool		below_outer_join;	/* is it below an outer join? */
+	Relids		qualscope;		/* base Relids syntactically included in this
+								 * jointree node */
+	Relids		inner_join_rels;	/* base Relids syntactically included in
+									 * inner joins appearing at or below this
+									 * jointree node */
+	Relids		left_rels;		/* if join node, Relids of the left side */
+	Relids		right_rels;		/* if join node, Relids of the right side */
+	Relids		nonnullable_rels;	/* if outer join, Relids of the
+									 * non-nullable side */
+	/* Fields filled during deconstruct_distribute: */
+	SpecialJoinInfo *sjinfo;	/* if outer join, its SpecialJoinInfo */
+} JoinTreeItem;
+
+/* Elements of the postponed_qual_list used during deconstruct_distribute */
 typedef struct PostponedQual
 {
 	Node	   *qual;			/* a qual clause waiting to be processed */
@@ -52,8 +85,9 @@ static void extract_lateral_references(PlannerInfo *root, RelOptInfo *brel,
 									   Index rtindex);
 static List *deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 								 bool below_outer_join,
-								 Relids *qualscope, Relids *inner_join_rels,
-								 List **postponed_qual_list);
+								 List **item_list);
+static void deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
+								   List **postponed_qual_list);
 static void process_security_barrier_quals(PlannerInfo *root,
 										   int rti, Relids qualscope,
 										   bool below_outer_join);
@@ -63,9 +97,17 @@ static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
 										   JoinType jointype, List *clause);
 static void compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo,
 								  List *clause);
+static void distribute_quals_to_rels(PlannerInfo *root, List *clauses,
+									 bool below_outer_join,
+									 SpecialJoinInfo *sjinfo,
+									 Index security_level,
+									 Relids qualscope,
+									 Relids ojscope,
+									 Relids outerjoin_nonnullable,
+									 List **postponed_qual_list);
 static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									bool below_outer_join,
-									JoinType jointype,
+									SpecialJoinInfo *sjinfo,
 									Index security_level,
 									Relids qualscope,
 									Relids ojscope,
@@ -683,9 +725,9 @@ List *
 deconstruct_jointree(PlannerInfo *root)
 {
 	List	   *result;
-	Relids		qualscope;
-	Relids		inner_join_rels;
+	List	   *item_list = NIL;
 	List	   *postponed_qual_list = NIL;
+	ListCell   *lc;
 
 	/*
 	 * After this point, no more PlaceHolderInfos may be made, because
@@ -699,98 +741,105 @@ deconstruct_jointree(PlannerInfo *root)
 	Assert(root->parse->jointree != NULL &&
 		   IsA(root->parse->jointree, FromExpr));
 
-	/* this is filled as we scan the jointree */
+	/* These are filled as we scan the jointree */
+	root->all_baserels = NULL;
 	root->nullable_baserels = NULL;
 
-	result = deconstruct_recurse(root, (Node *) root->parse->jointree, false,
-								 &qualscope, &inner_join_rels,
-								 &postponed_qual_list);
+	/* Perform the initial scan of the jointree */
+	result = deconstruct_recurse(root, (Node *) root->parse->jointree,
+								 false,
+								 &item_list);
 
-	/* Shouldn't be any leftover quals */
+	/* Now scan all the jointree nodes again, and distribute quals */
+	foreach(lc, item_list)
+	{
+		JoinTreeItem *jtitem = (JoinTreeItem *) lfirst(lc);
+
+		deconstruct_distribute(root, jtitem,
+							   &postponed_qual_list);
+	}
+
+	/* Shouldn't be any leftover postponed quals */
 	Assert(postponed_qual_list == NIL);
 
+	/* Don't need the JoinTreeItems any more */
+	list_free_deep(item_list);
+
 	return result;
 }
 
 /*
  * deconstruct_recurse
- *	  One recursion level of deconstruct_jointree processing.
+ *	  One recursion level of deconstruct_jointree's initial jointree scan.
  *
  * Inputs:
  *	jtnode is the jointree node to examine
  *	below_outer_join is true if this node is within the nullable side of a
  *		higher-level outer join
- * Outputs:
- *	*qualscope gets the set of base Relids syntactically included in this
- *		jointree node (do not modify or free this, as it may also be pointed
- *		to by RestrictInfo and SpecialJoinInfo nodes)
- *	*inner_join_rels gets the set of base Relids syntactically included in
- *		inner joins appearing at or below this jointree node (do not modify
- *		or free this, either)
- *	*postponed_qual_list is a list of PostponedQual structs, which we can
- *		add quals to if they turn out to belong to a higher join level
- *	Return value is the appropriate joinlist for this jointree node
  *
- * In addition, entries will be added to root->join_info_list for outer joins.
+ * item_list is an in/out parameter: we add a JoinTreeItem struct to
+ * that list for each jointree node, in depth-first traversal order.
+ * (Hence, after each call, the last list item corresponds to its jtnode.)
+ *
+ * Return value is the appropriate joinlist for this jointree node.
  */
 static List *
-deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
-					Relids *qualscope, Relids *inner_join_rels,
-					List **postponed_qual_list)
+deconstruct_recurse(PlannerInfo *root, Node *jtnode,
+					bool below_outer_join,
+					List **item_list)
 {
 	List	   *joinlist;
+	JoinTreeItem *jtitem;
+
+	Assert(jtnode != NULL);
+
+	/* Make the new JoinTreeItem, but don't add it to item_list yet */
+	jtitem = palloc0_object(JoinTreeItem);
+	jtitem->jtnode = jtnode;
+	jtitem->below_outer_join = below_outer_join;
 
-	if (jtnode == NULL)
-	{
-		*qualscope = NULL;
-		*inner_join_rels = NULL;
-		return NIL;
-	}
 	if (IsA(jtnode, RangeTblRef))
 	{
 		int			varno = ((RangeTblRef *) jtnode)->rtindex;
 
+		/* Fill all_baserels as we encounter baserel jointree nodes */
+		root->all_baserels = bms_add_member(root->all_baserels, varno);
 		/* qualscope is just the one RTE */
-		*qualscope = bms_make_singleton(varno);
-		/* Deal with any securityQuals attached to the RTE */
-		if (root->qual_security_level > 0)
-			process_security_barrier_quals(root,
-										   varno,
-										   *qualscope,
-										   below_outer_join);
+		jtitem->qualscope = bms_make_singleton(varno);
 		/* A single baserel does not create an inner join */
-		*inner_join_rels = NULL;
+		jtitem->inner_join_rels = NULL;
 		joinlist = list_make1(jtnode);
 	}
 	else if (IsA(jtnode, FromExpr))
 	{
 		FromExpr   *f = (FromExpr *) jtnode;
-		List	   *child_postponed_quals = NIL;
 		int			remaining;
 		ListCell   *l;
 
 		/*
-		 * First, recurse to handle child joins.  We collapse subproblems into
-		 * a single joinlist whenever the resulting joinlist wouldn't exceed
-		 * from_collapse_limit members.  Also, always collapse one-element
-		 * subproblems, since that won't lengthen the joinlist anyway.
+		 * Recurse to handle child nodes, and compute output joinlist.  We
+		 * collapse subproblems into a single joinlist whenever the resulting
+		 * joinlist wouldn't exceed from_collapse_limit members.  Also, always
+		 * collapse one-element subproblems, since that won't lengthen the
+		 * joinlist anyway.
 		 */
-		*qualscope = NULL;
-		*inner_join_rels = NULL;
+		jtitem->qualscope = NULL;
+		jtitem->inner_join_rels = NULL;
 		joinlist = NIL;
 		remaining = list_length(f->fromlist);
 		foreach(l, f->fromlist)
 		{
-			Relids		sub_qualscope;
+			JoinTreeItem *sub_item;
 			List	   *sub_joinlist;
 			int			sub_members;
 
 			sub_joinlist = deconstruct_recurse(root, lfirst(l),
 											   below_outer_join,
-											   &sub_qualscope,
-											   inner_join_rels,
-											   &child_postponed_quals);
-			*qualscope = bms_add_members(*qualscope, sub_qualscope);
+											   item_list);
+			sub_item = (JoinTreeItem *) llast(*item_list);
+			jtitem->qualscope = bms_add_members(jtitem->qualscope,
+												sub_item->qualscope);
+			jtitem->inner_join_rels = sub_item->inner_join_rels;
 			sub_members = list_length(sub_joinlist);
 			remaining--;
 			if (sub_members <= 1 ||
@@ -808,115 +857,80 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 		 * that still possible?) the initialization before the loop fixed it.
 		 */
 		if (list_length(f->fromlist) > 1)
-			*inner_join_rels = *qualscope;
-
-		/*
-		 * Try to process any quals postponed by children.  If they need
-		 * further postponement, add them to my output postponed_qual_list.
-		 */
-		foreach(l, child_postponed_quals)
-		{
-			PostponedQual *pq = (PostponedQual *) lfirst(l);
-
-			if (bms_is_subset(pq->relids, *qualscope))
-				distribute_qual_to_rels(root, pq->qual,
-										below_outer_join, JOIN_INNER,
-										root->qual_security_level,
-										*qualscope, NULL, NULL,
-										NULL);
-			else
-				*postponed_qual_list = lappend(*postponed_qual_list, pq);
-		}
-
-		/*
-		 * Now process the top-level quals.
-		 */
-		foreach(l, (List *) f->quals)
-		{
-			Node	   *qual = (Node *) lfirst(l);
-
-			distribute_qual_to_rels(root, qual,
-									below_outer_join, JOIN_INNER,
-									root->qual_security_level,
-									*qualscope, NULL, NULL,
-									postponed_qual_list);
-		}
+			jtitem->inner_join_rels = jtitem->qualscope;
 	}
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
-		List	   *child_postponed_quals = NIL;
-		Relids		leftids,
-					rightids,
-					left_inners,
-					right_inners,
-					nonnullable_rels,
-					nullable_rels,
-					ojscope;
+		Relids		nullable_rels;
+		JoinTreeItem *left_item,
+				   *right_item;
 		List	   *leftjoinlist,
 				   *rightjoinlist;
-		List	   *my_quals;
-		SpecialJoinInfo *sjinfo;
-		ListCell   *l;
 
-		/*
-		 * Order of operations here is subtle and critical.  First we recurse
-		 * to handle sub-JOINs.  Their join quals will be placed without
-		 * regard for whether this level is an outer join, which is correct.
-		 * Then we place our own join quals, which are restricted by lower
-		 * outer joins in any case, and are forced to this level if this is an
-		 * outer join and they mention the outer side.  Finally, if this is an
-		 * outer join, we create a join_info_list entry for the join.  This
-		 * will prevent quals above us in the join tree that use those rels
-		 * from being pushed down below this level.  (It's okay for upper
-		 * quals to be pushed down to the outer side, however.)
-		 */
 		switch (j->jointype)
 		{
 			case JOIN_INNER:
+				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
 												   below_outer_join,
-												   &leftids, &left_inners,
-												   &child_postponed_quals);
+												   item_list);
+				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
 													below_outer_join,
-													&rightids, &right_inners,
-													&child_postponed_quals);
-				*qualscope = bms_union(leftids, rightids);
-				*inner_join_rels = *qualscope;
+													item_list);
+				right_item = (JoinTreeItem *) llast(*item_list);
+				/* Compute qualscope etc */
+				jtitem->qualscope = bms_union(left_item->qualscope,
+											  right_item->qualscope);
+				jtitem->inner_join_rels = jtitem->qualscope;
+				jtitem->left_rels = left_item->qualscope;
+				jtitem->right_rels = right_item->qualscope;
 				/* Inner join adds no restrictions for quals */
-				nonnullable_rels = NULL;
+				jtitem->nonnullable_rels = NULL;
 				/* and it doesn't force anything to null, either */
 				nullable_rels = NULL;
 				break;
 			case JOIN_LEFT:
 			case JOIN_ANTI:
+				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
 												   below_outer_join,
-												   &leftids, &left_inners,
-												   &child_postponed_quals);
+												   item_list);
+				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
 													true,
-													&rightids, &right_inners,
-													&child_postponed_quals);
-				*qualscope = bms_union(leftids, rightids);
-				*inner_join_rels = bms_union(left_inners, right_inners);
-				nonnullable_rels = leftids;
-				nullable_rels = rightids;
+													item_list);
+				right_item = (JoinTreeItem *) llast(*item_list);
+				/* Compute qualscope etc */
+				jtitem->qualscope = bms_union(left_item->qualscope,
+											  right_item->qualscope);
+				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
+													right_item->inner_join_rels);
+				jtitem->left_rels = left_item->qualscope;
+				jtitem->right_rels = right_item->qualscope;
+				jtitem->nonnullable_rels = left_item->qualscope;
+				nullable_rels = right_item->qualscope;
 				break;
 			case JOIN_SEMI:
+				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
 												   below_outer_join,
-												   &leftids, &left_inners,
-												   &child_postponed_quals);
+												   item_list);
+				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
 													below_outer_join,
-													&rightids, &right_inners,
-													&child_postponed_quals);
-				*qualscope = bms_union(leftids, rightids);
-				*inner_join_rels = bms_union(left_inners, right_inners);
+													item_list);
+				right_item = (JoinTreeItem *) llast(*item_list);
+				/* Compute qualscope etc */
+				jtitem->qualscope = bms_union(left_item->qualscope,
+											  right_item->qualscope);
+				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
+													right_item->inner_join_rels);
+				jtitem->left_rels = left_item->qualscope;
+				jtitem->right_rels = right_item->qualscope;
 				/* Semi join adds no restrictions for quals */
-				nonnullable_rels = NULL;
+				jtitem->nonnullable_rels = NULL;
 
 				/*
 				 * Theoretically, a semijoin would null the RHS; but since the
@@ -926,27 +940,32 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 				nullable_rels = NULL;
 				break;
 			case JOIN_FULL:
+				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
 												   true,
-												   &leftids, &left_inners,
-												   &child_postponed_quals);
+												   item_list);
+				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
 													true,
-													&rightids, &right_inners,
-													&child_postponed_quals);
-				*qualscope = bms_union(leftids, rightids);
-				*inner_join_rels = bms_union(left_inners, right_inners);
+													item_list);
+				right_item = (JoinTreeItem *) llast(*item_list);
+				/* Compute qualscope etc */
+				jtitem->qualscope = bms_union(left_item->qualscope,
+											  right_item->qualscope);
+				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
+													right_item->inner_join_rels);
+				jtitem->left_rels = left_item->qualscope;
+				jtitem->right_rels = right_item->qualscope;
 				/* each side is both outer and inner */
-				nonnullable_rels = *qualscope;
-				nullable_rels = *qualscope;
+				jtitem->nonnullable_rels = jtitem->qualscope;
+				nullable_rels = jtitem->qualscope;
 				break;
 			default:
 				/* JOIN_RIGHT was eliminated during reduce_outer_joins() */
 				elog(ERROR, "unrecognized join type: %d",
 					 (int) j->jointype);
-				nonnullable_rels = NULL;	/* keep compiler quiet */
+				leftjoinlist = rightjoinlist = NIL; /* keep compiler quiet */
 				nullable_rels = NULL;
-				leftjoinlist = rightjoinlist = NIL;
 				break;
 		}
 
@@ -954,6 +973,131 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 		root->nullable_baserels = bms_add_members(root->nullable_baserels,
 												  nullable_rels);
 
+		/*
+		 * Compute the output joinlist.  We fold subproblems together except
+		 * at a FULL JOIN or where join_collapse_limit would be exceeded.
+		 */
+		if (j->jointype == JOIN_FULL)
+		{
+			/* force the join order exactly at this node */
+			joinlist = list_make1(list_make2(leftjoinlist, rightjoinlist));
+		}
+		else if (list_length(leftjoinlist) + list_length(rightjoinlist) <=
+				 join_collapse_limit)
+		{
+			/* OK to combine subproblems */
+			joinlist = list_concat(leftjoinlist, rightjoinlist);
+		}
+		else
+		{
+			/* can't combine, but needn't force join order above here */
+			Node	   *leftpart,
+					   *rightpart;
+
+			/* avoid creating useless 1-element sublists */
+			if (list_length(leftjoinlist) == 1)
+				leftpart = (Node *) linitial(leftjoinlist);
+			else
+				leftpart = (Node *) leftjoinlist;
+			if (list_length(rightjoinlist) == 1)
+				rightpart = (Node *) linitial(rightjoinlist);
+			else
+				rightpart = (Node *) rightjoinlist;
+			joinlist = list_make2(leftpart, rightpart);
+		}
+	}
+	else
+	{
+		elog(ERROR, "unrecognized node type: %d",
+			 (int) nodeTag(jtnode));
+		joinlist = NIL;			/* keep compiler quiet */
+	}
+
+	/* Finally, we can add the new JoinTreeItem to item_list */
+	*item_list = lappend(*item_list, jtitem);
+
+	return joinlist;
+}
+
+/*
+ * deconstruct_distribute
+ *	  Process one jointree node in phase 2 of deconstruct_jointree processing.
+ *
+ * Distribute quals of the node to appropriate restriction and join lists.
+ * In addition, entries will be added to root->join_info_list for outer joins.
+ *
+ * Inputs:
+ *	jtitem is the JoinTreeItem to examine
+ * Input/Outputs:
+ *	*postponed_qual_list is a list of PostponedQual structs
+ *
+ * On entry, *postponed_qual_list contains any quals that had to be postponed
+ * out of lower join levels (because they contain lateral references).
+ * On exit, *postponed_qual_list contains quals that can't be processed yet
+ * (because their lateral references are still unsatisfied).
+ */
+static void
+deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
+					   List **postponed_qual_list)
+{
+	Node	   *jtnode = jtitem->jtnode;
+
+	if (IsA(jtnode, RangeTblRef))
+	{
+		int			varno = ((RangeTblRef *) jtnode)->rtindex;
+
+		/* Deal with any securityQuals attached to the RTE */
+		if (root->qual_security_level > 0)
+			process_security_barrier_quals(root,
+										   varno,
+										   jtitem->qualscope,
+										   jtitem->below_outer_join);
+	}
+	else if (IsA(jtnode, FromExpr))
+	{
+		FromExpr   *f = (FromExpr *) jtnode;
+		List	   *new_postponed_quals = NIL;
+		ListCell   *l;
+
+		/*
+		 * Try to process any quals postponed by children.  If they need
+		 * further postponement, add them to my output postponed_qual_list.
+		 */
+		foreach(l, *postponed_qual_list)
+		{
+			PostponedQual *pq = (PostponedQual *) lfirst(l);
+
+			if (bms_is_subset(pq->relids, jtitem->qualscope))
+				distribute_qual_to_rels(root, pq->qual,
+										jtitem->below_outer_join,
+										NULL,
+										root->qual_security_level,
+										jtitem->qualscope, NULL, NULL,
+										NULL);
+			else
+				new_postponed_quals = lappend(new_postponed_quals, pq);
+		}
+		*postponed_qual_list = new_postponed_quals;
+
+		/*
+		 * Now process the top-level quals.
+		 */
+		distribute_quals_to_rels(root, (List *) f->quals,
+								 jtitem->below_outer_join,
+								 NULL,
+								 root->qual_security_level,
+								 jtitem->qualscope, NULL, NULL,
+								 postponed_qual_list);
+	}
+	else if (IsA(jtnode, JoinExpr))
+	{
+		JoinExpr   *j = (JoinExpr *) jtnode;
+		List	   *new_postponed_quals = NIL;
+		Relids		ojscope;
+		List	   *my_quals;
+		SpecialJoinInfo *sjinfo;
+		ListCell   *l;
+
 		/*
 		 * Try to process any quals postponed by children.  If they need
 		 * further postponement, add them to my output postponed_qual_list.
@@ -961,11 +1105,11 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 		 * that they'll be handled properly in make_outerjoininfo.
 		 */
 		my_quals = NIL;
-		foreach(l, child_postponed_quals)
+		foreach(l, *postponed_qual_list)
 		{
 			PostponedQual *pq = (PostponedQual *) lfirst(l);
 
-			if (bms_is_subset(pq->relids, *qualscope))
+			if (bms_is_subset(pq->relids, jtitem->qualscope))
 				my_quals = lappend(my_quals, pq->qual);
 			else
 			{
@@ -974,16 +1118,15 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 				 * If this Assert fires, pull_up_subqueries() messed up.
 				 */
 				Assert(j->jointype == JOIN_INNER);
-				*postponed_qual_list = lappend(*postponed_qual_list, pq);
+				new_postponed_quals = lappend(new_postponed_quals, pq);
 			}
 		}
+		*postponed_qual_list = new_postponed_quals;
 		my_quals = list_concat(my_quals, (List *) j->quals);
 
 		/*
-		 * For an OJ, form the SpecialJoinInfo now, because we need the OJ's
-		 * semantic scope (ojscope) to pass to distribute_qual_to_rels.  But
-		 * we mustn't add it to join_info_list just yet, because we don't want
-		 * distribute_qual_to_rels to think it is an outer join below us.
+		 * For an OJ, form the SpecialJoinInfo now, so that we can pass it to
+		 * distribute_qual_to_rels.  We must compute its ojscope too.
 		 *
 		 * Semijoins are a bit of a hybrid: we build a SpecialJoinInfo, but we
 		 * want ojscope = NULL for distribute_qual_to_rels.
@@ -991,15 +1134,19 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 		if (j->jointype != JOIN_INNER)
 		{
 			sjinfo = make_outerjoininfo(root,
-										leftids, rightids,
-										*inner_join_rels,
+										jtitem->left_rels,
+										jtitem->right_rels,
+										jtitem->inner_join_rels,
 										j->jointype,
 										my_quals);
+			jtitem->sjinfo = sjinfo;
 			if (j->jointype == JOIN_SEMI)
 				ojscope = NULL;
 			else
+			{
 				ojscope = bms_union(sjinfo->min_lefthand,
 									sjinfo->min_righthand);
+			}
 		}
 		else
 		{
@@ -1008,67 +1155,27 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode, bool below_outer_join,
 		}
 
 		/* Process the JOIN's qual clauses */
-		foreach(l, my_quals)
-		{
-			Node	   *qual = (Node *) lfirst(l);
-
-			distribute_qual_to_rels(root, qual,
-									below_outer_join, j->jointype,
-									root->qual_security_level,
-									*qualscope,
-									ojscope, nonnullable_rels,
-									postponed_qual_list);
-		}
-
-		/* Now we can add the SpecialJoinInfo to join_info_list */
+		distribute_quals_to_rels(root, my_quals,
+								 jtitem->below_outer_join,
+								 sjinfo,
+								 root->qual_security_level,
+								 jtitem->qualscope,
+								 ojscope, jtitem->nonnullable_rels,
+								 postponed_qual_list);
+
+		/* And add the SpecialJoinInfo to join_info_list */
 		if (sjinfo)
 		{
 			root->join_info_list = lappend(root->join_info_list, sjinfo);
 			/* Each time we do that, recheck placeholder eval levels */
 			update_placeholder_eval_levels(root, sjinfo);
 		}
-
-		/*
-		 * Finally, compute the output joinlist.  We fold subproblems together
-		 * except at a FULL JOIN or where join_collapse_limit would be
-		 * exceeded.
-		 */
-		if (j->jointype == JOIN_FULL)
-		{
-			/* force the join order exactly at this node */
-			joinlist = list_make1(list_make2(leftjoinlist, rightjoinlist));
-		}
-		else if (list_length(leftjoinlist) + list_length(rightjoinlist) <=
-				 join_collapse_limit)
-		{
-			/* OK to combine subproblems */
-			joinlist = list_concat(leftjoinlist, rightjoinlist);
-		}
-		else
-		{
-			/* can't combine, but needn't force join order above here */
-			Node	   *leftpart,
-					   *rightpart;
-
-			/* avoid creating useless 1-element sublists */
-			if (list_length(leftjoinlist) == 1)
-				leftpart = (Node *) linitial(leftjoinlist);
-			else
-				leftpart = (Node *) leftjoinlist;
-			if (list_length(rightjoinlist) == 1)
-				rightpart = (Node *) linitial(rightjoinlist);
-			else
-				rightpart = (Node *) rightjoinlist;
-			joinlist = list_make2(leftpart, rightpart);
-		}
 	}
 	else
 	{
 		elog(ERROR, "unrecognized node type: %d",
 			 (int) nodeTag(jtnode));
-		joinlist = NIL;			/* keep compiler quiet */
 	}
-	return joinlist;
 }
 
 /*
@@ -1102,27 +1209,21 @@ process_security_barrier_quals(PlannerInfo *root,
 	foreach(lc, rte->securityQuals)
 	{
 		List	   *qualset = (List *) lfirst(lc);
-		ListCell   *lc2;
-
-		foreach(lc2, qualset)
-		{
-			Node	   *qual = (Node *) lfirst(lc2);
 
-			/*
-			 * We cheat to the extent of passing ojscope = qualscope rather
-			 * than its more logical value of NULL.  The only effect this has
-			 * is to force a Var-free qual to be evaluated at the rel rather
-			 * than being pushed up to top of tree, which we don't want.
-			 */
-			distribute_qual_to_rels(root, qual,
-									below_outer_join,
-									JOIN_INNER,
-									security_level,
-									qualscope,
-									qualscope,
-									NULL,
-									NULL);
-		}
+		/*
+		 * We cheat to the extent of passing ojscope = qualscope rather than
+		 * its more logical value of NULL.  The only effect this has is to
+		 * force a Var-free qual to be evaluated at the rel rather than being
+		 * pushed up to top of tree, which we don't want.
+		 */
+		distribute_quals_to_rels(root, qualset,
+								 below_outer_join,
+								 NULL,
+								 security_level,
+								 qualscope,
+								 qualscope,
+								 NULL,
+								 NULL);
 		security_level++;
 	}
 
@@ -1572,6 +1673,38 @@ compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo, List *clause)
  *
  *****************************************************************************/
 
+/*
+ * distribute_quals_to_rels
+ *	  Convenience routine to apply distribute_qual_to_rels to each element
+ *	  of an AND'ed list of clauses.
+ */
+static void
+distribute_quals_to_rels(PlannerInfo *root, List *clauses,
+						 bool below_outer_join,
+						 SpecialJoinInfo *sjinfo,
+						 Index security_level,
+						 Relids qualscope,
+						 Relids ojscope,
+						 Relids outerjoin_nonnullable,
+						 List **postponed_qual_list)
+{
+	ListCell   *lc;
+
+	foreach(lc, clauses)
+	{
+		Node	   *clause = (Node *) lfirst(lc);
+
+		distribute_qual_to_rels(root, clause,
+								below_outer_join,
+								sjinfo,
+								security_level,
+								qualscope,
+								ojscope,
+								outerjoin_nonnullable,
+								postponed_qual_list);
+	}
+}
+
 /*
  * distribute_qual_to_rels
  *	  Add clause information to either the baserestrictinfo or joininfo list
@@ -1586,7 +1719,7 @@ compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo, List *clause)
  * 'clause': the qual clause to be distributed
  * 'below_outer_join': true if the qual is from a JOIN/ON that is below the
  *		nullable side of a higher-level outer join
- * 'jointype': type of join the qual is from (JOIN_INNER for a WHERE clause)
+ * 'sjinfo': join's SpecialJoinInfo (NULL for an inner join or WHERE clause)
  * 'security_level': security_level to assign to the qual
  * 'qualscope': set of baserels the qual's syntactic scope covers
  * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
@@ -1604,12 +1737,13 @@ compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo, List *clause)
  * level, which will be ojscope not necessarily qualscope.
  *
  * At the time this is called, root->join_info_list must contain entries for
- * all and only those special joins that are syntactically below this qual.
+ * all and only those special joins that are syntactically below this qual;
+ * in particular, the passed-in SpecialJoinInfo isn't yet in that list.
  */
 static void
 distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 						bool below_outer_join,
-						JoinType jointype,
+						SpecialJoinInfo *sjinfo,
 						Index security_level,
 						Relids qualscope,
 						Relids ojscope,
@@ -1646,7 +1780,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		PostponedQual *pq = (PostponedQual *) palloc(sizeof(PostponedQual));
 
 		Assert(root->hasLateralRTEs);	/* shouldn't happen otherwise */
-		Assert(jointype == JOIN_INNER); /* mustn't postpone past outer join */
+		Assert(sjinfo == NULL); /* mustn't postpone past outer join */
 		pq->qual = clause;
 		pq->relids = relids;
 		*postponed_qual_list = lappend(*postponed_qual_list, pq);
@@ -1930,14 +2064,19 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 			/* we need to set up left_ec/right_ec the hard way */
 			initialize_mergeclause_eclasses(root, restrictinfo);
 			/* now see if it should go to any outer-join lists */
+			Assert(sjinfo != NULL);
 			if (bms_is_subset(restrictinfo->left_relids,
 							  outerjoin_nonnullable) &&
 				!bms_overlap(restrictinfo->right_relids,
 							 outerjoin_nonnullable))
 			{
 				/* we have outervar = innervar */
+				OuterJoinClauseInfo *ojcinfo = makeNode(OuterJoinClauseInfo);
+
+				ojcinfo->rinfo = restrictinfo;
+				ojcinfo->sjinfo = sjinfo;
 				root->left_join_clauses = lappend(root->left_join_clauses,
-												  restrictinfo);
+												  ojcinfo);
 				return;
 			}
 			if (bms_is_subset(restrictinfo->right_relids,
@@ -1946,15 +2085,23 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 							 outerjoin_nonnullable))
 			{
 				/* we have innervar = outervar */
+				OuterJoinClauseInfo *ojcinfo = makeNode(OuterJoinClauseInfo);
+
+				ojcinfo->rinfo = restrictinfo;
+				ojcinfo->sjinfo = sjinfo;
 				root->right_join_clauses = lappend(root->right_join_clauses,
-												   restrictinfo);
+												   ojcinfo);
 				return;
 			}
-			if (jointype == JOIN_FULL)
+			if (sjinfo->jointype == JOIN_FULL)
 			{
 				/* FULL JOIN (above tests cannot match in this case) */
+				OuterJoinClauseInfo *ojcinfo = makeNode(OuterJoinClauseInfo);
+
+				ojcinfo->rinfo = restrictinfo;
+				ojcinfo->sjinfo = sjinfo;
 				root->full_join_clauses = lappend(root->full_join_clauses,
-												  restrictinfo);
+												  ojcinfo);
 				return;
 			}
 			/* nope, so fall through to distribute_restrictinfo_to_rels */
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
index 980f583915..6f51c7ee75 100644
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -40,6 +40,20 @@ typedef struct
 	int			win_location;
 } locate_windowfunc_context;
 
+typedef struct
+{
+	const Bitmapset *target_relids;
+	const Bitmapset *added_relids;
+	int			sublevels_up;
+} add_nulling_relids_context;
+
+typedef struct
+{
+	const Bitmapset *removable_relids;
+	const Bitmapset *except_relids;
+	int			sublevels_up;
+} remove_nulling_relids_context;
+
 static bool contain_aggs_of_level_walker(Node *node,
 										 contain_aggs_of_level_context *context);
 static bool locate_agg_of_level_walker(Node *node,
@@ -50,6 +64,10 @@ static bool locate_windowfunc_walker(Node *node,
 static bool checkExprHasSubLink_walker(Node *node, void *context);
 static Relids offset_relid_set(Relids relids, int offset);
 static Relids adjust_relid_set(Relids relids, int oldrelid, int newrelid);
+static Node *add_nulling_relids_mutator(Node *node,
+										add_nulling_relids_context *context);
+static Node *remove_nulling_relids_mutator(Node *node,
+										   remove_nulling_relids_context *context);

 /*
@@ -381,6 +399,8 @@ OffsetVarNodes_walker(Node *node, OffsetVarNodes_context *context)
 		if (var->varlevelsup == context->sublevels_up)
 		{
 			var->varno += context->offset;
+			var->varnullingrels = offset_relid_set(var->varnullingrels,
+												   context->offset);
 			if (var->varnosyn > 0)
 				var->varnosyn += context->offset;
 		}
@@ -419,6 +439,8 @@ OffsetVarNodes_walker(Node *node, OffsetVarNodes_context *context)
 		{
 			phv->phrels = offset_relid_set(phv->phrels,
 										   context->offset);
+			phv->phnullingrels = offset_relid_set(phv->phnullingrels,
+												  context->offset);
 		}
 		/* fall through to examine children */
 	}
@@ -543,11 +565,13 @@ ChangeVarNodes_walker(Node *node, ChangeVarNodes_context *context)
 	{
 		Var		   *var = (Var *) node;
 
-		if (var->varlevelsup == context->sublevels_up &&
-			var->varno == context->rt_index)
+		if (var->varlevelsup == context->sublevels_up)
 		{
-			var->varno = context->new_index;
-			/* If the syntactic referent is same RTE, fix it too */
+			if (var->varno == context->rt_index)
+				var->varno = context->new_index;
+			var->varnullingrels = adjust_relid_set(var->varnullingrels,
+												   context->rt_index,
+												   context->new_index);
 			if (var->varnosyn == context->rt_index)
 				var->varnosyn = context->new_index;
 		}
@@ -590,6 +614,9 @@ ChangeVarNodes_walker(Node *node, ChangeVarNodes_context *context)
 			phv->phrels = adjust_relid_set(phv->phrels,
 										   context->rt_index,
 										   context->new_index);
+			phv->phnullingrels = adjust_relid_set(phv->phnullingrels,
+												  context->rt_index,
+												  context->new_index);
 		}
 		/* fall through to examine children */
 	}
@@ -866,7 +893,8 @@ rangeTableEntry_used_walker(Node *node,
 		Var		   *var = (Var *) node;
 
 		if (var->varlevelsup == context->sublevels_up &&
-			var->varno == context->rt_index)
+			(var->varno == context->rt_index ||
+			 bms_is_member(context->rt_index, var->varnullingrels)))
 			return true;
 		return false;
 	}
@@ -1094,6 +1122,195 @@ AddInvertedQual(Query *parsetree, Node *qual)
 }

+/*
+ * add_nulling_relids() finds Vars and PlaceHolderVars that belong to any
+ * of the target_relids, and adds added_relids to their varnullingrels
+ * and phnullingrels fields.
+ */
+Node *
+add_nulling_relids(Node *node,
+				   const Bitmapset *target_relids,
+				   const Bitmapset *added_relids)
+{
+	add_nulling_relids_context context;
+
+	context.target_relids = target_relids;
+	context.added_relids = added_relids;
+	context.sublevels_up = 0;
+	return query_or_expression_tree_mutator(node,
+											add_nulling_relids_mutator,
+											&context,
+											0);
+}
+
+static Node *
+add_nulling_relids_mutator(Node *node,
+						   add_nulling_relids_context *context)
+{
+	if (node == NULL)
+		return NULL;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varlevelsup == context->sublevels_up &&
+			bms_is_member(var->varno, context->target_relids))
+		{
+			Relids		newnullingrels = bms_union(var->varnullingrels,
+												   context->added_relids);
+
+			/* Copy the Var ... */
+			var = copyObject(var);
+			/* ... and replace the copy's varnullingrels field */
+			var->varnullingrels = newnullingrels;
+			return (Node *) var;
+		}
+		/* Otherwise fall through to copy the Var normally */
+	}
+	else if (IsA(node, PlaceHolderVar))
+	{
+		PlaceHolderVar *phv = (PlaceHolderVar *) node;
+
+		if (phv->phlevelsup == context->sublevels_up &&
+			bms_overlap(phv->phrels, context->target_relids))
+		{
+			Relids		newnullingrels = bms_union(phv->phnullingrels,
+												   context->added_relids);
+
+			/*
+			 * We don't modify the contents of the PHV's expression, only add
+			 * to phnullingrels.  This corresponds to assuming that the PHV
+			 * will be evaluated at the same level as before, then perhaps be
+			 * nulled as it bubbles up.  Hence, just flat-copy the node ...
+			 */
+			phv = makeNode(PlaceHolderVar);
+			memcpy(phv, node, sizeof(PlaceHolderVar));
+			/* ... and replace the copy's phnullingrels field */
+			phv->phnullingrels = newnullingrels;
+			return (Node *) phv;
+		}
+		/* Otherwise fall through to copy the PlaceHolderVar normally */
+	}
+	else if (IsA(node, Query))
+	{
+		/* Recurse into RTE or sublink subquery */
+		Query	   *newnode;
+
+		context->sublevels_up++;
+		newnode = query_tree_mutator((Query *) node,
+									 add_nulling_relids_mutator,
+									 (void *) context,
+									 0);
+		context->sublevels_up--;
+		return (Node *) newnode;
+	}
+	return expression_tree_mutator(node, add_nulling_relids_mutator,
+								   (void *) context);
+}
+
+/*
+ * remove_nulling_relids() removes mentions of the specified RT index(es)
+ * in Var.varnullingrels and PlaceHolderVar.phnullingrels fields within
+ * the given expression, except in nodes belonging to rels listed in
+ * except_relids.
+ */
+Node *
+remove_nulling_relids(Node *node,
+					  const Bitmapset *removable_relids,
+					  const Bitmapset *except_relids)
+{
+	remove_nulling_relids_context context;
+
+	context.removable_relids = removable_relids;
+	context.except_relids = except_relids;
+	context.sublevels_up = 0;
+	return query_or_expression_tree_mutator(node,
+											remove_nulling_relids_mutator,
+											&context,
+											0);
+}
+
+static Node *
+remove_nulling_relids_mutator(Node *node,
+							  remove_nulling_relids_context *context)
+{
+	if (node == NULL)
+		return NULL;
+	if (IsA(node, Var))
+	{
+		Var		   *var = (Var *) node;
+
+		if (var->varlevelsup == context->sublevels_up &&
+			!bms_is_member(var->varno, context->except_relids) &&
+			bms_overlap(var->varnullingrels, context->removable_relids))
+		{
+			Relids		newnullingrels = bms_difference(var->varnullingrels,
+														context->removable_relids);
+
+			/* Micro-optimization: ensure nullingrels is NULL if empty */
+			if (bms_is_empty(newnullingrels))
+				newnullingrels = NULL;
+			/* Copy the Var ... */
+			var = copyObject(var);
+			/* ... and replace the copy's varnullingrels field */
+			var->varnullingrels = newnullingrels;
+			return (Node *) var;
+		}
+		/* Otherwise fall through to copy the Var normally */
+	}
+	else if (IsA(node, PlaceHolderVar))
+	{
+		PlaceHolderVar *phv = (PlaceHolderVar *) node;
+
+		if (phv->phlevelsup == context->sublevels_up &&
+			!bms_overlap(phv->phrels, context->except_relids))
+		{
+			Relids		newnullingrels = bms_difference(phv->phnullingrels,
+														context->removable_relids);
+
+			/*
+			 * Micro-optimization: ensure nullingrels is NULL if empty.
+			 *
+			 * Note: it might seem desirable to remove the PHV altogether if
+			 * phnullingrels goes to empty.  Currently we dare not do that
+			 * because we use PHVs in some cases to enforce separate identity
+			 * of subexpressions; see wrap_non_vars usages in prepjointree.c.
+			 */
+			if (bms_is_empty(newnullingrels))
+				newnullingrels = NULL;
+			/* Copy the PlaceHolderVar and mutate what's below ... */
+			phv = (PlaceHolderVar *)
+				expression_tree_mutator(node,
+										remove_nulling_relids_mutator,
+										(void *) context);
+			/* ... and replace the copy's phnullingrels field */
+			phv->phnullingrels = newnullingrels;
+			/* We must also update phrels, if it contains a removable RTI */
+			phv->phrels = bms_difference(phv->phrels,
+										 context->removable_relids);
+			Assert(!bms_is_empty(phv->phrels));
+			return (Node *) phv;
+		}
+		/* Otherwise fall through to copy the PlaceHolderVar normally */
+	}
+	else if (IsA(node, Query))
+	{
+		/* Recurse into RTE or sublink subquery */
+		Query	   *newnode;
+
+		context->sublevels_up++;
+		newnode = query_tree_mutator((Query *) node,
+									 remove_nulling_relids_mutator,
+									 (void *) context,
+									 0);
+		context->sublevels_up--;
+		return (Node *) newnode;
+	}
+	return expression_tree_mutator(node, remove_nulling_relids_mutator,
+								   (void *) context);
+}
+
+
 /*
  * replace_rte_variables() finds all Vars in an expression tree
  * that reference a particular RTE, and replaces them with substitute
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 2d1d8f4bcd..0909420615 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -249,10 +249,8 @@ struct PlannerInfo
 	struct AppendRelInfo **append_rel_array pg_node_attr(read_write_ignore);
 
 	/*
-	 * all_baserels is a Relids set of all base relids (but not "other"
-	 * relids) in the query; that is, the Relids identifier of the final join
-	 * we need to form.  This is computed in make_one_rel, just before we
-	 * start making Paths.
+	 * all_baserels is a Relids set of all base relids (but not joins or
+	 * "other" rels) in the query.  This is computed in deconstruct_jointree.
 	 */
 	Relids		all_baserels;
 
@@ -313,19 +311,19 @@ struct PlannerInfo
 	List	   *canon_pathkeys;
 
 	/*
-	 * list of RestrictInfos for mergejoinable outer join clauses
+	 * list of OuterJoinClauseInfos for mergejoinable outer join clauses
 	 * w/nonnullable var on left
 	 */
 	List	   *left_join_clauses;
 
 	/*
-	 * list of RestrictInfos for mergejoinable outer join clauses
+	 * list of OuterJoinClauseInfos for mergejoinable outer join clauses
 	 * w/nonnullable var on right
 	 */
 	List	   *right_join_clauses;
 
 	/*
-	 * list of RestrictInfos for mergejoinable full join clauses
+	 * list of OuterJoinClauseInfos for mergejoinable full join clauses
 	 */
 	List	   *full_join_clauses;
 
@@ -911,7 +909,7 @@ typedef struct RelOptInfo
 	int32	   *attr_widths pg_node_attr(read_write_ignore);
 	/* LATERAL Vars and PHVs referenced by rel */
 	List	   *lateral_vars;
-	/* rels that reference me laterally */
+	/* rels that reference this baserel laterally */
 	Relids		lateral_referencers;
 	/* list of IndexOptInfo */
 	List	   *indexlist;
@@ -921,10 +919,7 @@ typedef struct RelOptInfo
 	BlockNumber pages;
 	Cardinality tuples;
 	double		allvisfrac;
-
-	/*
-	 * Indexes in PlannerInfo's eq_classes list of ECs that mention this rel
-	 */
+	/* indexes in PlannerInfo's eq_classes list of ECs that mention this rel */
 	Bitmapset  *eclass_indexes;
 	PlannerInfo *subroot;		/* if subquery */
 	List	   *subplan_params; /* if subquery */
@@ -2624,10 +2619,15 @@ typedef struct MergeScanSelCache
  * of a plan tree.  This is used during planning to represent the contained
  * expression.  At the end of the planning process it is replaced by either
  * the contained expression or a Var referring to a lower-level evaluation of
- * the contained expression.  Typically the evaluation occurs below an outer
+ * the contained expression.  Generally the evaluation occurs below an outer
  * join, and Var references above the outer join might thereby yield NULL
  * instead of the expression value.
  *
+ * phrels and phlevelsup correspond to the varno/varlevelsup fields of a
+ * plain Var, except that phrels has to be a relid set since the evaluation
+ * level of a PlaceHolderVar might be a join rather than a base relation.
+ * Likewise, phnullingrels corresponds to varnullingrels.
+ *
  * Although the planner treats this as an expression node type, it is not
  * recognized by the parser or executor, so we declare it here rather than
  * in primnodes.h.
@@ -2640,8 +2640,10 @@ typedef struct MergeScanSelCache
  * PHV.  Another way in which it can happen is that initplan sublinks
  * could get replaced by differently-numbered Params when sublink folding
  * is done.  (The end result of such a situation would be some
- * unreferenced initplans, which is annoying but not really a problem.) On
- * the same reasoning, there is no need to examine phrels.
+ * unreferenced initplans, which is annoying but not really a problem.)
+ * On the same reasoning, there is no need to examine phrels.  But we do
+ * need to compare phnullingrels, as that represents effects that are
+ * external to the original value of the PHV.
  */
 
 typedef struct PlaceHolderVar
@@ -2651,9 +2653,12 @@ typedef struct PlaceHolderVar
 	/* the represented expression */
 	Expr	   *phexpr pg_node_attr(equal_ignore);
 
-	/* base relids syntactically within expr src */
+	/* base+OJ relids syntactically within expr src */
 	Relids		phrels pg_node_attr(equal_ignore);
 
+	/* RT indexes of outer joins that can null PHV's value */
+	Relids		phnullingrels;
+
 	/* ID for PHV (unique within planner run) */
 	Index		phid;
 
@@ -2742,6 +2747,21 @@ struct SpecialJoinInfo
 	List	   *semi_rhs_exprs; /* righthand-side expressions of these ops */
 };
 
+/*
+ * Transient outer-join clause info.
+ *
+ * We set aside every outer join ON clause that looks mergejoinable,
+ * and process it specially at the end of qual distribution.
+ */
+typedef struct OuterJoinClauseInfo
+{
+	pg_node_attr(no_copy_equal, no_read)
+
+	NodeTag		type;
+	RestrictInfo *rinfo;		/* a mergejoinable outer-join clause */
+	SpecialJoinInfo *sjinfo;	/* the outer join's SpecialJoinInfo */
+} OuterJoinClauseInfo;
+
 /*
  * Append-relation info.
  *
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index dec7d5c775..6c96fa2f51 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -190,6 +190,14 @@ typedef struct Expr
  * row identity information during UPDATE/DELETE/MERGE.  This value should
  * never be seen outside the planner.
  *
+ * varnullingrels is the set of RT indexes of outer joins that can force
+ * the Var's value to null (at the point where it appears in the query).
+ * See optimizer/README for discussion of that.
+ *
+ * varlevelsup is greater than zero in Vars that represent outer references.
+ * Note that it affects the meaning of all of varno, varnullingrels, and
+ * varnosyn, all of which refer to the range table of that query level.
+ *
  * In the parser, varnosyn and varattnosyn are either identical to
  * varno/varattno, or they specify the column's position in an aliased JOIN
  * RTE that hides the semantic referent RTE's refname.  This is a syntactic
@@ -232,6 +240,8 @@ typedef struct Var
 	int32		vartypmod;
 	/* OID of collation, or InvalidOid if none */
 	Oid			varcollid;
+	/* RT indexes of outer joins that can replace the Var's value with null */
+	Bitmapset  *varnullingrels;
 
 	/*
 	 * for subquery variables referencing outer relations; 0 in a normal var,
diff --git a/src/include/rewrite/rewriteManip.h b/src/include/rewrite/rewriteManip.h
index 02d130cc26..365061fff4 100644
--- a/src/include/rewrite/rewriteManip.h
+++ b/src/include/rewrite/rewriteManip.h
@@ -65,6 +65,13 @@ extern bool contain_windowfuncs(Node *node);
 extern int	locate_windowfunc(Node *node);
 extern bool checkExprHasSubLink(Node *node);
 
+extern Node *add_nulling_relids(Node *node,
+								const Bitmapset *target_relids,
+								const Bitmapset *added_relids);
+extern Node *remove_nulling_relids(Node *node,
+								   const Bitmapset *removable_relids,
+								   const Bitmapset *except_relids);
+
 extern Node *replace_rte_variables(Node *node,
 								   int target_varno, int sublevels_up,
 								   replace_rte_variables_callback callback,
commit ec26da36b009833381f94baffb4bd649ad89fc71
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:26:56 2023 -0500

    Teach the parser to fill Var.varnullingrels correctly.
    
    Vars emitted by the parser are now marked with RT indexes of outer
    joins that can null them.  (This is done purely according to the
    syntax of the query; we don't consider whether an outer join could
    be strength-reduced, for example.)
    
    Although the result of this step compiles, it will fail some
    regression tests due to the planner not yet knowing what to do.

diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 4a817b75ad..e892df9819 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -676,6 +676,7 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 		sub_pstate->p_rtable = sub_rtable;
 		sub_pstate->p_rteperminfos = sub_rteperminfos;
 		sub_pstate->p_joinexprs = NIL;	/* sub_rtable has no joins */
+		sub_pstate->p_nullingrels = NIL;
 		sub_pstate->p_namespace = sub_namespace;
 		sub_pstate->p_resolve_unknowns = false;
 
@@ -857,7 +858,7 @@ transformInsertStmt(ParseState *pstate, InsertStmt *stmt)
 		/*
 		 * Generate list of Vars referencing the RTE
 		 */
-		exprList = expandNSItemVars(nsitem, 0, -1, NULL);
+		exprList = expandNSItemVars(pstate, nsitem, 0, -1, NULL);
 
 		/*
 		 * Re-apply any indirection on the target column specs to the Vars
diff --git a/src/backend/parser/parse_clause.c b/src/backend/parser/parse_clause.c
index bafa5bb381..f61f794755 100644
--- a/src/backend/parser/parse_clause.c
+++ b/src/backend/parser/parse_clause.c
@@ -52,7 +52,8 @@
 #include "utils/syscache.h"

-static int	extractRemainingColumns(ParseNamespaceColumn *src_nscolumns,
+static int	extractRemainingColumns(ParseState *pstate,
+									ParseNamespaceColumn *src_nscolumns,
 									List *src_colnames,
 									List **src_colnos,
 									List **res_colnames, List **res_colvars,
@@ -75,9 +76,11 @@ static ParseNamespaceItem *getNSItemForSpecialRelationTypes(ParseState *pstate,
 static Node *transformFromClauseItem(ParseState *pstate, Node *n,
 									 ParseNamespaceItem **top_nsitem,
 									 List **namespace);
-static Var *buildVarFromNSColumn(ParseNamespaceColumn *nscol);
+static Var *buildVarFromNSColumn(ParseState *pstate,
+								 ParseNamespaceColumn *nscol);
 static Node *buildMergedJoinVar(ParseState *pstate, JoinType jointype,
 								Var *l_colvar, Var *r_colvar);
+static void markRelsAsNulledBy(ParseState *pstate, Node *n, int jindex);
 static void setNamespaceColumnVisibility(List *namespace, bool cols_visible);
 static void setNamespaceLateralState(List *namespace,
 									 bool lateral_only, bool lateral_ok);
@@ -251,7 +254,8 @@ setTargetTable(ParseState *pstate, RangeVar *relation,
  * Returns the number of columns added.
  */
 static int
-extractRemainingColumns(ParseNamespaceColumn *src_nscolumns,
+extractRemainingColumns(ParseState *pstate,
+						ParseNamespaceColumn *src_nscolumns,
 						List *src_colnames,
 						List **src_colnos,
 						List **res_colnames, List **res_colvars,
@@ -287,7 +291,8 @@ extractRemainingColumns(ParseNamespaceColumn *src_nscolumns,
 			*src_colnos = lappend_int(*src_colnos, attnum);
 			*res_colnames = lappend(*res_colnames, lfirst(lc));
 			*res_colvars = lappend(*res_colvars,
-								   buildVarFromNSColumn(src_nscolumns + attnum - 1));
+								   buildVarFromNSColumn(pstate,
+														src_nscolumns + attnum - 1));
 			/* Copy the input relation's nscolumn data for this column */
 			res_nscolumns[colcount] = src_nscolumns[attnum - 1];
 			colcount++;
@@ -1288,8 +1293,7 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 		{
 			/*
 			 * JOIN/USING (or NATURAL JOIN, as transformed above). Transform
-			 * the list into an explicit ON-condition, and generate a list of
-			 * merged result columns.
+			 * the list into an explicit ON-condition.
 			 */
 			List	   *ucols = j->usingClause;
 			List	   *l_usingvars = NIL;
@@ -1307,8 +1311,6 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 				int			r_index = -1;
 				Var		   *l_colvar,
 						   *r_colvar;
-				Node	   *u_colvar;
-				ParseNamespaceColumn *res_nscolumn;
 
 				Assert(u_colname[0] != '\0');
 
@@ -1372,17 +1374,109 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 									u_colname)));
 				r_colnos = lappend_int(r_colnos, r_index + 1);
 
-				l_colvar = buildVarFromNSColumn(l_nscolumns + l_index);
+				/* Build Vars to use in the generated JOIN ON clause */
+				l_colvar = buildVarFromNSColumn(pstate, l_nscolumns + l_index);
 				l_usingvars = lappend(l_usingvars, l_colvar);
-				r_colvar = buildVarFromNSColumn(r_nscolumns + r_index);
+				r_colvar = buildVarFromNSColumn(pstate, r_nscolumns + r_index);
 				r_usingvars = lappend(r_usingvars, r_colvar);
 
+				/*
+				 * While we're here, add column names to the res_colnames
+				 * list.  It's a bit ugly to do this here while the
+				 * corresponding res_colvars entries are not made till later,
+				 * but doing this later would require an additional traversal
+				 * of the usingClause list.
+				 */
 				res_colnames = lappend(res_colnames, lfirst(ucol));
+			}
+
+			/* Construct the generated JOIN ON clause */
+			j->quals = transformJoinUsingClause(pstate,
+												l_usingvars,
+												r_usingvars);
+		}
+		else if (j->quals)
+		{
+			/* User-written ON-condition; transform it */
+			j->quals = transformJoinOnClause(pstate, j, my_namespace);
+		}
+		else
+		{
+			/* CROSS JOIN: no quals */
+		}
+
+		/*
+		 * If this is an outer join, now mark the appropriate child RTEs as
+		 * being nulled by this join.  We have finished processing the child
+		 * join expressions as well as the current join's quals, which deal in
+		 * non-nulled input columns.  All future references to those RTEs will
+		 * see possibly-nulled values, and we should mark generated Vars to
+		 * account for that.  In particular, the join alias Vars that we're
+		 * about to build should reflect the nulling effects of this join.
+		 *
+		 * A difficulty with doing this is that we need the join's RT index,
+		 * which we don't officially have yet.  However, no other RTE can get
+		 * made between here and the addRangeTableEntryForJoin call, so we can
+		 * predict what the assignment will be.  (Alternatively, we could call
+		 * addRangeTableEntryForJoin before we have all the data computed, but
+		 * this seems less ugly.)
+		 */
+		j->rtindex = list_length(pstate->p_rtable) + 1;
+
+		switch (j->jointype)
+		{
+			case JOIN_INNER:
+				break;
+			case JOIN_LEFT:
+				markRelsAsNulledBy(pstate, j->rarg, j->rtindex);
+				break;
+			case JOIN_FULL:
+				markRelsAsNulledBy(pstate, j->larg, j->rtindex);
+				markRelsAsNulledBy(pstate, j->rarg, j->rtindex);
+				break;
+			case JOIN_RIGHT:
+				markRelsAsNulledBy(pstate, j->larg, j->rtindex);
+				break;
+			default:
+				/* shouldn't see any other types here */
+				elog(ERROR, "unrecognized join type: %d",
+					 (int) j->jointype);
+				break;
+		}
+
+		/*
+		 * Now we can construct join alias expressions for the USING columns.
+		 */
+		if (j->usingClause)
+		{
+			ListCell   *lc1,
+					   *lc2;
+
+			/* Scan the colnos lists to recover info from the previous loop */
+			forboth(lc1, l_colnos, lc2, r_colnos)
+			{
+				int			l_index = lfirst_int(lc1) - 1;
+				int			r_index = lfirst_int(lc2) - 1;
+				Var		   *l_colvar,
+						   *r_colvar;
+				Node	   *u_colvar;
+				ParseNamespaceColumn *res_nscolumn;
+
+				/*
+				 * Note we re-build these Vars: they might have different
+				 * varnullingrels than the ones made in the previous loop.
+				 */
+				l_colvar = buildVarFromNSColumn(pstate, l_nscolumns + l_index);
+				r_colvar = buildVarFromNSColumn(pstate, r_nscolumns + r_index);
+
+				/* Construct the join alias Var for this column */
 				u_colvar = buildMergedJoinVar(pstate,
 											  j->jointype,
 											  l_colvar,
 											  r_colvar);
 				res_colvars = lappend(res_colvars, u_colvar);
+
+				/* Construct column's res_nscolumns[] entry */
 				res_nscolumn = res_nscolumns + res_colindex;
 				res_colindex++;
 				if (u_colvar == (Node *) l_colvar)
@@ -1400,47 +1494,45 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 					/*
 					 * Merged column is not semantically equivalent to either
 					 * input, so it needs to be referenced as the join output
-					 * column.  We don't know the join's varno yet, so we'll
-					 * replace these zeroes below.
+					 * column.
 					 */
-					res_nscolumn->p_varno = 0;
+					res_nscolumn->p_varno = j->rtindex;
 					res_nscolumn->p_varattno = res_colindex;
 					res_nscolumn->p_vartype = exprType(u_colvar);
 					res_nscolumn->p_vartypmod = exprTypmod(u_colvar);
 					res_nscolumn->p_varcollid = exprCollation(u_colvar);
-					res_nscolumn->p_varnosyn = 0;
+					res_nscolumn->p_varnosyn = j->rtindex;
 					res_nscolumn->p_varattnosyn = res_colindex;
 				}
 			}
-
-			j->quals = transformJoinUsingClause(pstate,
-												l_usingvars,
-												r_usingvars);
-		}
-		else if (j->quals)
-		{
-			/* User-written ON-condition; transform it */
-			j->quals = transformJoinOnClause(pstate, j, my_namespace);
-		}
-		else
-		{
-			/* CROSS JOIN: no quals */
 		}
 
 		/* Add remaining columns from each side to the output columns */
 		res_colindex +=
-			extractRemainingColumns(l_nscolumns, l_colnames, &l_colnos,
+			extractRemainingColumns(pstate,
+									l_nscolumns, l_colnames, &l_colnos,
 									&res_colnames, &res_colvars,
 									res_nscolumns + res_colindex);
 		res_colindex +=
-			extractRemainingColumns(r_nscolumns, r_colnames, &r_colnos,
+			extractRemainingColumns(pstate,
+									r_nscolumns, r_colnames, &r_colnos,
 									&res_colnames, &res_colvars,
 									res_nscolumns + res_colindex);
 
+		/* If join has an alias, it syntactically hides all inputs */
+		if (j->alias)
+		{
+			for (k = 0; k < res_colindex; k++)
+			{
+				ParseNamespaceColumn *nscol = res_nscolumns + k;
+
+				nscol->p_varnosyn = j->rtindex;
+				nscol->p_varattnosyn = k + 1;
+			}
+		}
+
 		/*
 		 * Now build an RTE and nsitem for the result of the join.
-		 * res_nscolumns isn't totally done yet, but that's OK because
-		 * addRangeTableEntryForJoin doesn't examine it, only store a pointer.
 		 */
 		nsitem = addRangeTableEntryForJoin(pstate,
 										   res_colnames,
@@ -1454,31 +1546,16 @@ transformFromClauseItem(ParseState *pstate, Node *n,
 										   j->alias,
 										   true);
 
-		j->rtindex = nsitem->p_rtindex;
+		/* Verify that we correctly predicted the join's RT index */
+		Assert(j->rtindex == nsitem->p_rtindex);
+		/* Cross-check number of columns, too */
+		Assert(res_colindex == list_length(nsitem->p_names->colnames));
 
 		/*
-		 * Now that we know the join RTE's rangetable index, we can fix up the
-		 * res_nscolumns data in places where it should contain that.
+		 * Save a link to the JoinExpr in the proper element of p_joinexprs.
+		 * Since we maintain that list lazily, it may be necessary to fill in
+		 * empty entries before we can add the JoinExpr in the right place.
 		 */
-		Assert(res_colindex == list_length(nsitem->p_names->colnames));
-		for (k = 0; k < res_colindex; k++)
-		{
-			ParseNamespaceColumn *nscol = res_nscolumns + k;
-
-			/* fill in join RTI for merged columns */
-			if (nscol->p_varno == 0)
-				nscol->p_varno = j->rtindex;
-			if (nscol->p_varnosyn == 0)
-				nscol->p_varnosyn = j->rtindex;
-			/* if join has an alias, it syntactically hides all inputs */
-			if (j->alias)
-			{
-				nscol->p_varnosyn = j->rtindex;
-				nscol->p_varattnosyn = k + 1;
-			}
-		}
-
-		/* make a matching link to the JoinExpr for later use */
 		for (k = list_length(pstate->p_joinexprs) + 1; k < j->rtindex; k++)
 			pstate->p_joinexprs = lappend(pstate->p_joinexprs, NULL);
 		pstate->p_joinexprs = lappend(pstate->p_joinexprs, j);
@@ -1547,10 +1624,13 @@ transformFromClauseItem(ParseState *pstate, Node *n,
  * buildVarFromNSColumn -
  *	  build a Var node using ParseNamespaceColumn data
  *
- * We assume varlevelsup should be 0, and no location is specified
+ * This is used to construct joinaliasvars entries.
+ * We can assume varlevelsup should be 0, and no location is specified.
+ * Note also that no column SELECT privilege is requested here; that would
+ * happen only if the column is actually referenced in the query.
  */
 static Var *
-buildVarFromNSColumn(ParseNamespaceColumn *nscol)
+buildVarFromNSColumn(ParseState *pstate, ParseNamespaceColumn *nscol)
 {
 	Var		   *var;
 
@@ -1564,6 +1644,10 @@ buildVarFromNSColumn(ParseNamespaceColumn *nscol)
 	/* makeVar doesn't offer parameters for these, so set by hand: */
 	var->varnosyn = nscol->p_varnosyn;
 	var->varattnosyn = nscol->p_varattnosyn;
+
+	/* ... and update varnullingrels */
+	markNullableIfNeeded(pstate, var);
+
 	return var;
 }
 
@@ -1675,6 +1759,47 @@ buildMergedJoinVar(ParseState *pstate, JoinType jointype,
 	return res_node;
 }
 
+/*
+ * markRelsAsNulledBy -
+ *	  Mark the given jointree node and its children as nulled by join jindex
+ */
+static void
+markRelsAsNulledBy(ParseState *pstate, Node *n, int jindex)
+{
+	int			varno;
+	ListCell   *lc;
+
+	/* Note: we can't see FromExpr here */
+	if (IsA(n, RangeTblRef))
+	{
+		varno = ((RangeTblRef *) n)->rtindex;
+	}
+	else if (IsA(n, JoinExpr))
+	{
+		JoinExpr   *j = (JoinExpr *) n;
+
+		/* recurse to children */
+		markRelsAsNulledBy(pstate, j->larg, jindex);
+		markRelsAsNulledBy(pstate, j->rarg, jindex);
+		varno = j->rtindex;
+	}
+	else
+	{
+		elog(ERROR, "unrecognized node type: %d", (int) nodeTag(n));
+		varno = 0;				/* keep compiler quiet */
+	}
+
+	/*
+	 * Now add jindex to the p_nullingrels set for relation varno.  Since we
+	 * maintain the p_nullingrels list lazily, we might need to extend it to
+	 * make the varno'th entry exist.
+	 */
+	while (list_length(pstate->p_nullingrels) < varno)
+		pstate->p_nullingrels = lappend(pstate->p_nullingrels, NULL);
+	lc = list_nth_cell(pstate->p_nullingrels, varno - 1);
+	lfirst(lc) = bms_add_member((Bitmapset *) lfirst(lc), jindex);
+}
+
 /*
  * setNamespaceColumnVisibility -
  *	  Convenience subroutine to update cols_visible flags in a namespace list.
diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index 34757da0fa..52787b6794 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -1042,7 +1042,7 @@ coerce_record_to_complex(ParseState *pstate, Node *node,
 		ParseNamespaceItem *nsitem;
 
 		nsitem = GetNSItemByRangeTablePosn(pstate, rtindex, sublevels_up);
-		args = expandNSItemVars(nsitem, sublevels_up, vlocation, NULL);
+		args = expandNSItemVars(pstate, nsitem, sublevels_up, vlocation, NULL);
 	}
 	else
 		ereport(ERROR,
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 53e904ca6d..7ff41acb84 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -2478,6 +2478,9 @@ transformWholeRowRef(ParseState *pstate, ParseNamespaceItem *nsitem,
 		/* location is not filled in by makeWholeRowVar */
 		result->location = location;
 
+		/* mark Var if it's nulled by any outer joins */
+		markNullableIfNeeded(pstate, result);
+
 		/* mark relation as requiring whole-row SELECT access */
 		markVarForSelectPriv(pstate, result);
 
@@ -2505,6 +2508,8 @@ transformWholeRowRef(ParseState *pstate, ParseNamespaceItem *nsitem,
 		rowexpr->colnames = copyObject(nsitem->p_names->colnames);
 		rowexpr->location = location;
 
+		/* XXX we ought to mark the row as possibly nullable */
+
 		return (Node *) rowexpr;
 	}
 }
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index b490541f03..52b4a6e89d 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -763,6 +763,9 @@ scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
 	}
 	var->location = location;
 
+	/* Mark Var if it's nulled by any outer joins */
+	markNullableIfNeeded(pstate, var);
+
 	/* Require read access to the column */
 	markVarForSelectPriv(pstate, var);
 
@@ -1023,6 +1026,35 @@ searchRangeTableForCol(ParseState *pstate, const char *alias, const char *colnam
 	return fuzzystate;
 }
 
+/*
+ * markNullableIfNeeded
+ *		If the RTE referenced by the Var is nullable by outer join(s)
+ *		at this point in the query, set var->varnullingrels to show that.
+ */
+void
+markNullableIfNeeded(ParseState *pstate, Var *var)
+{
+	int			rtindex = var->varno;
+	Bitmapset  *relids;
+
+	/* Find the appropriate pstate */
+	for (int lv = 0; lv < var->varlevelsup; lv++)
+		pstate = pstate->parentParseState;
+
+	/* Find currently-relevant join relids for the Var's rel */
+	if (rtindex > 0 && rtindex <= list_length(pstate->p_nullingrels))
+		relids = (Bitmapset *) list_nth(pstate->p_nullingrels, rtindex - 1);
+	else
+		relids = NULL;
+
+	/*
+	 * Merge with any already-declared nulling rels.  (Typically there won't
+	 * be any, but let's get it right if there are.)
+	 */
+	if (relids != NULL)
+		var->varnullingrels = bms_union(var->varnullingrels, relids);
+}
+
 /*
  * markRTEForSelectPriv
  *	   Mark the specified column of the RTE with index rtindex
@@ -3087,7 +3119,7 @@ expandTupleDesc(TupleDesc tupdesc, Alias *eref, int count, int offset,
  * the list elements mustn't be modified.
  */
 List *
-expandNSItemVars(ParseNamespaceItem *nsitem,
+expandNSItemVars(ParseState *pstate, ParseNamespaceItem *nsitem,
 				 int sublevels_up, int location,
 				 List **colnames)
 {
@@ -3123,6 +3155,10 @@ expandNSItemVars(ParseNamespaceItem *nsitem,
 			var->varnosyn = nscol->p_varnosyn;
 			var->varattnosyn = nscol->p_varattnosyn;
 			var->location = location;
+
+			/* ... and update varnullingrels */
+			markNullableIfNeeded(pstate, var);
+
 			result = lappend(result, var);
 			if (colnames)
 				*colnames = lappend(*colnames, colnameval);
@@ -3158,7 +3194,7 @@ expandNSItemAttrs(ParseState *pstate, ParseNamespaceItem *nsitem,
 			   *var;
 	List	   *te_list = NIL;
 
-	vars = expandNSItemVars(nsitem, sublevels_up, location, &names);
+	vars = expandNSItemVars(pstate, nsitem, sublevels_up, location, &names);
 
 	/*
 	 * Require read access to the table.  This is normally redundant with the
diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
index 0ca6beccb8..25781db5c1 100644
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@@ -1371,7 +1371,7 @@ ExpandSingleTable(ParseState *pstate, ParseNamespaceItem *nsitem,
 		List	   *vars;
 		ListCell   *l;
 
-		vars = expandNSItemVars(nsitem, sublevels_up, location, NULL);
+		vars = expandNSItemVars(pstate, nsitem, sublevels_up, location, NULL);
 
 		/*
 		 * Require read access to the table.  This is normally redundant with
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 89335d95e7..fbbbe647a4 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1090,6 +1090,14 @@ typedef struct RangeTblEntry
 	 * alias Vars are generated only for merged columns).  We keep these
 	 * entries only because they're needed in expandRTE() and similar code.
 	 *
+	 * Vars appearing within joinaliasvars are marked with varnullingrels sets
+	 * that describe the nulling effects of this join and lower ones.  This is
+	 * essential for FULL JOIN cases, because the COALESCE expression only
+	 * describes the semantics correctly if its inputs have been nulled by the
+	 * join.  For other cases, it allows expandRTE() to generate a valid
+	 * representation of the join's output without consulting additional
+	 * parser state.
+	 *
 	 * Within a Query loaded from a stored rule, it is possible for non-merged
 	 * joinaliasvars items to be null pointers, which are placeholders for
 	 * (necessarily unreferenced) columns dropped since the rule was made.
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 1a3792236a..f589112d5e 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -118,6 +118,13 @@ typedef Node *(*CoerceParamHook) (ParseState *pstate, Param *param,
  * This is one-for-one with p_rtable, but contains NULLs for non-join
  * RTEs, and may be shorter than p_rtable if the last RTE(s) aren't joins.
  *
+ * p_nullingrels: list of Bitmapsets associated with p_rtable entries, each
+ * containing the set of outer-join RTE indexes that can null that relation
+ * at the current point in the parse tree.  This is one-for-one with p_rtable,
+ * but may be shorter than p_rtable, in which case the missing entries are
+ * implicitly empty (NULL).  That rule allows us to save work when the query
+ * contains no outer joins.
+ *
  * p_joinlist: list of join items (RangeTblRef and JoinExpr nodes) that
  * will become the fromlist of the query's top-level FromExpr node.
  *
@@ -187,6 +194,7 @@ struct ParseState
 	List	   *p_rteperminfos; /* list of RTEPermissionInfo nodes for each
 								 * RTE_RELATION entry in rtable */
 	List	   *p_joinexprs;	/* JoinExprs for RTE_JOIN p_rtable entries */
+	List	   *p_nullingrels;	/* Bitmapsets showing nulling outer joins */
 	List	   *p_joinlist;		/* join items so far (will become FromExpr
 								 * node's fromlist) */
 	List	   *p_namespace;	/* currently-referenceable RTEs (List of
diff --git a/src/include/parser/parse_relation.h b/src/include/parser/parse_relation.h
index dfa584b6ac..67d9b1e412 100644
--- a/src/include/parser/parse_relation.h
+++ b/src/include/parser/parse_relation.h
@@ -41,6 +41,7 @@ extern Node *scanNSItemForColumn(ParseState *pstate, ParseNamespaceItem *nsitem,
 								 int location);
 extern Node *colNameToVar(ParseState *pstate, const char *colname, bool localonly,
 						  int location);
+extern void markNullableIfNeeded(ParseState *pstate, Var *var);
 extern void markVarForSelectPriv(ParseState *pstate, Var *var);
 extern Relation parserOpenTable(ParseState *pstate, const RangeVar *relation,
 								int lockmode);
@@ -113,7 +114,7 @@ extern void errorMissingColumn(ParseState *pstate,
 extern void expandRTE(RangeTblEntry *rte, int rtindex, int sublevels_up,
 					  int location, bool include_dropped,
 					  List **colnames, List **colvars);
-extern List *expandNSItemVars(ParseNamespaceItem *nsitem,
+extern List *expandNSItemVars(ParseState *pstate, ParseNamespaceItem *nsitem,
 							  int sublevels_up, int location,
 							  List **colnames);
 extern List *expandNSItemAttrs(ParseState *pstate, ParseNamespaceItem *nsitem,
commit 2f8421adf64e6ec4d3701ded2f6cb99cdd47eaec
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:31:10 2023 -0500

    Teach the planner to cope with Vars bearing nullingrels.
    
    The core idea of this step is to include varnullingrels in the
    relid sets that qual clauses are considered to depend on.
    So that we can still easily compare quals' relids to RelOptInfos'
    relids, that means also adding outer join relids to the identifying
    relids of join relations.  Much of the bulk of this step is concerned
    with fallout from the latter change.
    
    I've resolved the previous squishiness entailed by outer join identity 3
    by generating multiple versions of outer-join quals that could get moved
    to a join level where they need to contain different nullingrels sets.
    Now we have versions of such quals with the correct nullingrels for
    each level where they could appear.
    
    This requires a bit of new mechanism (RestrictInfo.has_clone/is_clone)
    to prevent multiple versions of the same qual from getting used in the
    plan.  My worry about how that could work with EquivalenceClasses is
    resolved by creating EquivalenceClasses only from the least-marked
    version of a qual.  (This doesn't really lose anything, since versions
    with more nullingrels bits don't correspond to any equalities available
    outside the nest of commuting outer joins.)
    
    These extra versions of quals would also result in generating multiple
    parameterized paths that differ only in what nullingrels they expect
    for the Vars from the parameterization rel(s).  That seems like it'd
    be very wasteful, so I've arranged to generate such paths only from
    the least-marked version of a qual (the has_clone version).
    
    Unlike in the previous version of this patch, setrefs.c is able to
    cross-check the nullingrel sets of most Vars and PlaceHolderVars to
    ensure that they match up with what the previous plan step produces.
    But there are three cases that I've so far punted on:
    1. The targetlist and qpqual of an outer join node will contain
    nullingrels bits for the outer join itself.  To check exact matching to
    the input, we'd need to know the OJ's relid as well as which input(s)
    got nulled, neither of which is cheaply available in setrefs.c.  For
    now, it's just checking that such Vars have a superset of the input's
    nullingrels bits.
    2. Parameterized paths will generally refer to the least-marked version
    of whichever outer-side Vars they use, which may not be what's actually
    available from the outside of the nestloop.  (We're relying on the join
    ordering rules for that to be sensible.)  Again, setrefs.c is in no
    position to pass judgment on correctness, so it's just checking that
    the parameter expression has a subset of the outer-side marking.
    3. Row identity variables are not marked with any nullingrels, which
    may not correspond to reality.  I've punted on this by skipping the
    checks when varattno <= 0.
    Point 1 could be addressed if we were willing to add informational
    fields to join plan nodes, which might be worth doing, but I'm not sure.
    The other two points seem like the extra mechanisms needed for a
    bulletproof check would be considerably more trouble than they'd be
    worth.
    
    There is still some confusion about which versions of a cloned qual
    are actually necessary to check, which results in some extra filter
    conditions showing up in a couple of regression test plans.  There are
    also some failure cases involving full joins that remain to be fixed.
    This patch is already mighty big, so I'll address those failures
    separately.
    
    This step removes some low-hanging fruit from the old implementation,
    such as the need to track lowest_nulling_outer_join during subquery
    pullup.  There's much more to do in that line, though.

diff --git a/src/backend/optimizer/geqo/geqo_eval.c b/src/backend/optimizer/geqo/geqo_eval.c
index 6d5d1a7eb2..a694ac4a13 100644
--- a/src/backend/optimizer/geqo/geqo_eval.c
+++ b/src/backend/optimizer/geqo/geqo_eval.c
@@ -273,7 +273,7 @@ merge_clump(PlannerInfo *root, List *clumps, Clump *new_clump, int num_gene,
 				 * rel once we know the final targetlist (see
 				 * grouping_planner).
 				 */
-				if (!bms_equal(joinrel->relids, root->all_baserels))
+				if (!bms_equal(joinrel->relids, root->all_query_rels))
 					generate_useful_gather_paths(root, joinrel, false);
 
 				/* Find and save the cheapest paths for this joinrel */
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index c56d3f926d..26b294d5d0 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -211,9 +211,9 @@ make_one_rel(PlannerInfo *root, List *joinlist)
 	rel = make_rel_from_joinlist(root, joinlist);
 
 	/*
-	 * The result should join all and only the query's base rels.
+	 * The result should join all and only the query's base + outer-join rels.
 	 */
-	Assert(bms_equal(rel->relids, root->all_baserels));
+	Assert(bms_equal(rel->relids, root->all_query_rels));
 
 	return rel;
 }
@@ -538,7 +538,7 @@ set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
 	 * the final scan/join targetlist is available (see grouping_planner).
 	 */
 	if (rel->reloptkind == RELOPT_BASEREL &&
-		!bms_equal(rel->relids, root->all_baserels))
+		!bms_equal(rel->relids, root->all_query_rels))
 		generate_useful_gather_paths(root, rel, false);
 
 	/* Now find the cheapest of the paths for this rel */
@@ -859,7 +859,7 @@ set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *
 	 * to support an uncommon usage of second-rate sampling methods.  Instead,
 	 * if there is a risk that the query might perform an unsafe join, just
 	 * wrap the SampleScan in a Materialize node.  We can check for joins by
-	 * counting the membership of all_baserels (note that this correctly
+	 * counting the membership of all_query_rels (note that this correctly
 	 * counts inheritance trees as single rels).  If we're inside a subquery,
 	 * we can't easily check whether a join might occur in the outer query, so
 	 * just assume one is possible.
@@ -868,7 +868,7 @@ set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *
 	 * so check repeatable_across_scans last, even though that's a bit odd.
 	 */
 	if ((root->query_level > 1 ||
-		 bms_membership(root->all_baserels) != BMS_SINGLETON) &&
+		 bms_membership(root->all_query_rels) != BMS_SINGLETON) &&
 		!(GetTsmRoutine(rte->tablesample->tsmhandler)->repeatable_across_scans))
 	{
 		path = (Path *) create_material_path(rel, path);
@@ -950,7 +950,7 @@ set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
 	if (enable_partitionwise_join &&
 		rel->reloptkind == RELOPT_BASEREL &&
 		rte->relkind == RELKIND_PARTITIONED_TABLE &&
-		rel->attr_needed[InvalidAttrNumber - rel->min_attr] == NULL)
+		bms_is_empty(rel->attr_needed[InvalidAttrNumber - rel->min_attr]))
 		rel->consider_partitionwise_join = true;
 
 	/*
@@ -3409,7 +3409,7 @@ standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
 			 * partial paths.  We'll do the same for the topmost scan/join rel
 			 * once we know the final targetlist (see grouping_planner).
 			 */
-			if (!bms_equal(rel->relids, root->all_baserels))
+			if (!bms_equal(rel->relids, root->all_query_rels))
 				generate_useful_gather_paths(root, rel, false);
 
 			/* Find and save the cheapest paths for this rel */
diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 929a231112..61db6ad951 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -218,7 +218,7 @@ clauselist_selectivity_ext(PlannerInfo *root,
 
 			if (rinfo)
 			{
-				ok = (bms_membership(rinfo->clause_relids) == BMS_SINGLETON) &&
+				ok = (rinfo->num_base_rels == 1) &&
 					(is_pseudo_constant_clause_relids(lsecond(expr->args),
 													  rinfo->right_relids) ||
 					 (varonleft = false,
@@ -579,30 +579,6 @@ find_single_rel_for_clauses(PlannerInfo *root, List *clauses)
 	return NULL;				/* no clauses */
 }
 
-/*
- * bms_is_subset_singleton
- *
- * Same result as bms_is_subset(s, bms_make_singleton(x)),
- * but a little faster and doesn't leak memory.
- *
- * Is this of use anywhere else?  If so move to bitmapset.c ...
- */
-static bool
-bms_is_subset_singleton(const Bitmapset *s, int x)
-{
-	switch (bms_membership(s))
-	{
-		case BMS_EMPTY_SET:
-			return true;
-		case BMS_SINGLETON:
-			return bms_is_member(x, s);
-		case BMS_MULTIPLE:
-			return false;
-	}
-	/* can't get here... */
-	return false;
-}
-
 /*
  * treat_as_join_clause -
  *	  Decide whether an operator clause is to be handled by the
@@ -631,17 +607,20 @@ treat_as_join_clause(PlannerInfo *root, Node *clause, RestrictInfo *rinfo,
 	else
 	{
 		/*
-		 * Otherwise, it's a join if there's more than one relation used. We
-		 * can optimize this calculation if an rinfo was passed.
+		 * Otherwise, it's a join if there's more than one base relation used.
+		 * We can optimize this calculation if an rinfo was passed.
 		 *
 		 * XXX	Since we know the clause is being evaluated at a join, the
 		 * only way it could be single-relation is if it was delayed by outer
-		 * joins.  Although we can make use of the restriction qual estimators
-		 * anyway, it seems likely that we ought to account for the
-		 * probability of injected nulls somehow.
+		 * joins.  We intentionally count only baserels here, not OJs that
+		 * might be present in rinfo->clause_relids, so that we direct such
+		 * cases to the restriction qual estimators not join estimators.
+		 * Eventually some notice should be taken of the possibility of
+		 * injected nulls, but we'll likely want to do that in the restriction
+		 * estimators rather than starting to treat such cases as join quals.
 		 */
 		if (rinfo)
-			return (bms_membership(rinfo->clause_relids) == BMS_MULTIPLE);
+			return (rinfo->num_base_rels > 1);
 		else
 			return (NumRelids(root, clause) > 1);
 	}
@@ -754,7 +733,9 @@ clause_selectivity_ext(PlannerInfo *root,
 		 * for all non-JOIN_INNER cases.
 		 */
 		if (varRelid == 0 ||
-			bms_is_subset_singleton(rinfo->clause_relids, varRelid))
+			rinfo->num_base_rels == 0 ||
+			(rinfo->num_base_rels == 1 &&
+			 bms_is_member(varRelid, rinfo->clause_relids)))
 		{
 			/* Cacheable --- do we already have the result? */
 			if (jointype == JOIN_INNER)
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 29ae32d960..7d957a47a4 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -4781,6 +4781,10 @@ compute_semi_anti_join_factors(PlannerInfo *root,
 	norm_sjinfo.syn_lefthand = outerrel->relids;
 	norm_sjinfo.syn_righthand = innerrel->relids;
 	norm_sjinfo.jointype = JOIN_INNER;
+	norm_sjinfo.ojrelid = 0;
+	norm_sjinfo.commute_above_l = NULL;
+	norm_sjinfo.commute_above_r = NULL;
+	norm_sjinfo.commute_below = NULL;
 	/* we don't bother trying to make the remaining fields valid */
 	norm_sjinfo.lhs_strict = false;
 	norm_sjinfo.delay_upper_joins = false;
@@ -4946,6 +4950,10 @@ approx_tuple_count(PlannerInfo *root, JoinPath *path, List *quals)
 	sjinfo.syn_lefthand = path->outerjoinpath->parent->relids;
 	sjinfo.syn_righthand = path->innerjoinpath->parent->relids;
 	sjinfo.jointype = JOIN_INNER;
+	sjinfo.ojrelid = 0;
+	sjinfo.commute_above_l = NULL;
+	sjinfo.commute_above_r = NULL;
+	sjinfo.commute_below = NULL;
 	/* we don't bother trying to make the remaining fields valid */
 	sjinfo.lhs_strict = false;
 	sjinfo.delay_upper_joins = false;
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 783ef5aa29..bfde80e8a4 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -29,6 +29,7 @@
 #include "optimizer/paths.h"
 #include "optimizer/planmain.h"
 #include "optimizer/restrictinfo.h"
+#include "rewrite/rewriteManip.h"
 #include "utils/lsyscache.h"

@@ -757,6 +758,12 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 		{
 			RelOptInfo *rel = root->simple_rel_array[i];
 
+			if (rel == NULL)	/* must be an outer join */
+			{
+				Assert(bms_is_member(i, root->outer_join_rels));
+				continue;
+			}
+
 			Assert(rel->reloptkind == RELOPT_BASEREL ||
 				   rel->reloptkind == RELOPT_DEADREL);
 
@@ -1113,6 +1120,12 @@ generate_base_implied_equalities(PlannerInfo *root)
 		{
 			RelOptInfo *rel = root->simple_rel_array[i];
 
+			if (rel == NULL)	/* must be an outer join */
+			{
+				Assert(bms_is_member(i, root->outer_join_rels));
+				continue;
+			}
+
 			Assert(rel->reloptkind == RELOPT_BASEREL);
 
 			rel->eclass_indexes = bms_add_member(rel->eclass_indexes,
@@ -2195,6 +2208,8 @@ static bool
 reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 {
 	RestrictInfo *rinfo = ojcinfo->rinfo;
+	SpecialJoinInfo *sjinfo = ojcinfo->sjinfo;
+	Relids		fjrelids = bms_make_singleton(sjinfo->ojrelid);
 	Expr	   *leftvar;
 	Expr	   *rightvar;
 	Oid			opno,
@@ -2276,6 +2291,18 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 				cfirst = (Node *) linitial(cexpr->args);
 				csecond = (Node *) lsecond(cexpr->args);
 
+				/*
+				 * The COALESCE arguments will be marked as possibly nulled by
+				 * the full join, while we wish to generate clauses that apply
+				 * to the join's inputs.  So we must strip the join from the
+				 * nullingrels fields of cfirst/csecond before comparing them
+				 * to leftvar/rightvar.  (Perhaps with a less hokey
+				 * representation for FULL JOIN USING output columns, this
+				 * wouldn't be needed?)
+				 */
+				cfirst = remove_nulling_relids(cfirst, fjrelids, NULL);
+				csecond = remove_nulling_relids(csecond, fjrelids, NULL);
+
 				if (equal(leftvar, cfirst) && equal(rightvar, csecond))
 				{
 					coal_idx = foreach_current_index(lc2);
@@ -3212,6 +3239,12 @@ get_eclass_indexes_for_relids(PlannerInfo *root, Relids relids)
 	{
 		RelOptInfo *rel = root->simple_rel_array[i];
 
+		if (rel == NULL)		/* must be an outer join */
+		{
+			Assert(bms_is_member(i, root->outer_join_rels));
+			continue;
+		}
+
 		ec_indexes = bms_add_members(ec_indexes, rel->eclass_indexes);
 	}
 	return ec_indexes;
diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index e13c8f1914..e9b784bcab 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -3352,13 +3352,13 @@ check_index_predicates(PlannerInfo *root, RelOptInfo *rel)
 	 * Add on any equivalence-derivable join clauses.  Computing the correct
 	 * relid sets for generate_join_implied_equalities is slightly tricky
 	 * because the rel could be a child rel rather than a true baserel, and in
-	 * that case we must remove its parents' relid(s) from all_baserels.
+	 * that case we must subtract its parents' relid(s) from all_query_rels.
 	 */
 	if (rel->reloptkind == RELOPT_OTHER_MEMBER_REL)
-		otherrels = bms_difference(root->all_baserels,
+		otherrels = bms_difference(root->all_query_rels,
 								   find_childrel_parents(root, rel));
 	else
-		otherrels = bms_difference(root->all_baserels, rel->relids);
+		otherrels = bms_difference(root->all_query_rels, rel->relids);
 
 	if (!bms_is_empty(otherrels))
 		clauselist =
@@ -3736,7 +3736,8 @@ match_index_to_operand(Node *operand,
 		 */
 		if (operand && IsA(operand, Var) &&
 			index->rel->relid == ((Var *) operand)->varno &&
-			indkey == ((Var *) operand)->varattno)
+			indkey == ((Var *) operand)->varattno &&
+			((Var *) operand)->varnullingrels == NULL)
 			return true;
 	}
 	else
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index d345c0437a..7591a7d81d 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -234,7 +234,9 @@ add_paths_to_joinrel(PlannerInfo *root,
 	 * reduces the number of parameterized paths we have to deal with at
 	 * higher join levels, without compromising the quality of the resulting
 	 * plan.  We express the restriction as a Relids set that must overlap the
-	 * parameterization of any proposed join path.
+	 * parameterization of any proposed join path.  Note: param_source_rels
+	 * should contain only baserels, not OJ relids, so starting from
+	 * all_baserels not all_query_rels is correct.
 	 */
 	foreach(lc, root->join_info_list)
 	{
@@ -365,6 +367,47 @@ allow_star_schema_join(PlannerInfo *root,
 			bms_nonempty_difference(inner_paramrels, outerrelids));
 }
 
+/*
+ * If the parameterization is only partly satisfied by the outer rel,
+ * the unsatisfied part can't include any outer-join relids that could
+ * null rels of the satisfied part.  That would imply that we're trying
+ * to use a clause involving a Var with nonempty varnullingrels at
+ * a join level where that value isn't yet computable.
+ */
+static inline bool
+have_unsafe_outer_join_ref(PlannerInfo *root,
+						   Relids outerrelids,
+						   Relids inner_paramrels)
+{
+	bool		result = false;
+	Relids		unsatisfied = bms_difference(inner_paramrels, outerrelids);
+
+	if (bms_overlap(unsatisfied, root->outer_join_rels))
+	{
+		ListCell   *lc;
+
+		foreach(lc, root->join_info_list)
+		{
+			SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+
+			if (!bms_is_member(sjinfo->ojrelid, unsatisfied))
+				continue;		/* not relevant */
+			if (bms_overlap(inner_paramrels, sjinfo->min_righthand) ||
+				(sjinfo->jointype == JOIN_FULL &&
+				 bms_overlap(inner_paramrels, sjinfo->min_lefthand)))
+			{
+				result = true;	/* doesn't work */
+				break;
+			}
+		}
+	}
+
+	/* Waste no memory when we reject a path here */
+	bms_free(unsatisfied);
+
+	return result;
+}
+
 /*
  * paraminfo_get_equal_hashops
  *		Determine if param_info and innerrel's lateral_vars can be hashed.
@@ -657,15 +700,16 @@ try_nestloop_path(PlannerInfo *root,
 	/*
 	 * Check to see if proposed path is still parameterized, and reject if the
 	 * parameterization wouldn't be sensible --- unless allow_star_schema_join
-	 * says to allow it anyway.  Also, we must reject if have_dangerous_phv
-	 * doesn't like the look of it, which could only happen if the nestloop is
-	 * still parameterized.
+	 * says to allow it anyway.  Also, we must reject if either
+	 * have_unsafe_outer_join_ref or have_dangerous_phv don't like the look of
+	 * it, which could only happen if the nestloop is still parameterized.
 	 */
 	required_outer = calc_nestloop_required_outer(outerrelids, outer_paramrels,
 												  innerrelids, inner_paramrels);
 	if (required_outer &&
 		((!bms_overlap(required_outer, extra->param_source_rels) &&
 		  !allow_star_schema_join(root, outerrelids, inner_paramrels)) ||
+		 have_unsafe_outer_join_ref(root, outerrelids, inner_paramrels) ||
 		 have_dangerous_phv(root, outerrelids, inner_paramrels)))
 	{
 		/* Waste no memory when we reject a path here */
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 9a5930ce86..56dd1073c5 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -353,7 +353,10 @@ make_rels_by_clauseless_joins(PlannerInfo *root,
  *
  * Caller must supply not only the two rels, but the union of their relids.
  * (We could simplify the API by computing joinrelids locally, but this
- * would be redundant work in the normal path through make_join_rel.)
+ * would be redundant work in the normal path through make_join_rel.
+ * Note that this value does NOT include the RT index of any outer join that
+ * might need to be performed here, so it's not the canonical identifier
+ * of the join relation.)
  *
  * On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
  * else it's set to point to the associated SpecialJoinInfo node.  Also,
@@ -695,7 +698,7 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
 	/* We should never try to join two overlapping sets of rels. */
 	Assert(!bms_overlap(rel1->relids, rel2->relids));
 
-	/* Construct Relids set that identifies the joinrel. */
+	/* Construct Relids set that identifies the joinrel (without OJ as yet). */
 	joinrelids = bms_union(rel1->relids, rel2->relids);
 
 	/* Check validity and determine join type. */
@@ -707,6 +710,10 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
 		return NULL;
 	}
 
+	/* If we have an outer join, add its RTI to form the canonical relids. */
+	if (sjinfo && sjinfo->ojrelid != 0)
+		joinrelids = bms_add_member(joinrelids, sjinfo->ojrelid);
+
 	/* Swap rels if needed to match the join info. */
 	if (reversed)
 	{
@@ -730,6 +737,10 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
 		sjinfo->syn_lefthand = rel1->relids;
 		sjinfo->syn_righthand = rel2->relids;
 		sjinfo->jointype = JOIN_INNER;
+		sjinfo->ojrelid = 0;
+		sjinfo->commute_above_l = NULL;
+		sjinfo->commute_above_r = NULL;
+		sjinfo->commute_below = NULL;
 		/* we don't bother trying to make the remaining fields valid */
 		sjinfo->lhs_strict = false;
 		sjinfo->delay_upper_joins = false;
@@ -1510,8 +1521,6 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 
 		/* We should never try to join two overlapping sets of rels. */
 		Assert(!bms_overlap(child_rel1->relids, child_rel2->relids));
-		child_joinrelids = bms_union(child_rel1->relids, child_rel2->relids);
-		appinfos = find_appinfos_by_relids(root, child_joinrelids, &nappinfos);
 
 		/*
 		 * Construct SpecialJoinInfo from parent join relations's
@@ -1521,6 +1530,15 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 											   child_rel1->relids,
 											   child_rel2->relids);
 
+		/* Build correct join relids for child join */
+		child_joinrelids = bms_union(child_rel1->relids, child_rel2->relids);
+		if (child_sjinfo->ojrelid != 0)
+			child_joinrelids = bms_add_member(child_joinrelids,
+											  child_sjinfo->ojrelid);
+
+		/* Find the AppendRelInfo structures */
+		appinfos = find_appinfos_by_relids(root, child_joinrelids, &nappinfos);
+
 		/*
 		 * Construct restrictions applicable to the child join from those
 		 * applicable to the parent join.
@@ -1536,8 +1554,7 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 		{
 			child_joinrel = build_child_join_rel(root, child_rel1, child_rel2,
 												 joinrel, child_restrictlist,
-												 child_sjinfo,
-												 child_sjinfo->jointype);
+												 child_sjinfo);
 			joinrel->part_rels[cnt_parts] = child_joinrel;
 			joinrel->live_parts = bms_add_member(joinrel->live_parts, cnt_parts);
 			joinrel->all_partrels = bms_add_members(joinrel->all_partrels,
@@ -1583,6 +1600,7 @@ build_child_join_sjinfo(PlannerInfo *root, SpecialJoinInfo *parent_sjinfo,
 	sjinfo->syn_righthand = adjust_child_relids(sjinfo->syn_righthand,
 												right_nappinfos,
 												right_appinfos);
+	/* outer-join relids need no adjustment */
 	sjinfo->semi_rhs_exprs = (List *) adjust_appendrel_attrs(root,
 															 (Node *) sjinfo->semi_rhs_exprs,
 															 right_nappinfos,
diff --git a/src/backend/optimizer/path/tidpath.c b/src/backend/optimizer/path/tidpath.c
index 6de994480b..05ad585a8f 100644
--- a/src/backend/optimizer/path/tidpath.c
+++ b/src/backend/optimizer/path/tidpath.c
@@ -59,6 +59,7 @@ IsCTIDVar(Var *var, RelOptInfo *rel)
 	if (var->varattno == SelfItemPointerAttributeNumber &&
 		var->vartype == TIDOID &&
 		var->varno == rel->relid &&
+		var->varnullingrels == NULL &&
 		var->varlevelsup == 0)
 		return true;
 	return false;
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 51b653fed4..fbb652e7b0 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -34,7 +34,7 @@
 
 /* local functions */
 static bool join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo);
-static void remove_rel_from_query(PlannerInfo *root, int relid,
+static void remove_rel_from_query(PlannerInfo *root, int relid, int ojrelid,
 								  Relids joinrelids);
 static List *remove_rel_from_joinlist(List *joinlist, int relid, int *nremoved);
 static bool rel_supports_distinctness(PlannerInfo *root, RelOptInfo *rel);
@@ -70,6 +70,7 @@ restart:
 	foreach(lc, root->join_info_list)
 	{
 		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+		Relids		joinrelids;
 		int			innerrelid;
 		int			nremoved;
 
@@ -84,9 +85,12 @@ restart:
 		 */
 		innerrelid = bms_singleton_member(sjinfo->min_righthand);
 
-		remove_rel_from_query(root, innerrelid,
-							  bms_union(sjinfo->min_lefthand,
-										sjinfo->min_righthand));
+		/* Compute the relid set for the join we are considering */
+		joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+		if (sjinfo->ojrelid != 0)
+			joinrelids = bms_add_member(joinrelids, sjinfo->ojrelid);
+
+		remove_rel_from_query(root, innerrelid, sjinfo->ojrelid, joinrelids);
 
 		/* We verify that exactly one reference gets removed from joinlist */
 		nremoved = 0;
@@ -188,6 +192,8 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 
 	/* Compute the relid set for the join we are considering */
 	joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+	if (sjinfo->ojrelid != 0)
+		joinrelids = bms_add_member(joinrelids, sjinfo->ojrelid);
 
 	/*
 	 * We can't remove the join if any inner-rel attributes are used above the
@@ -247,6 +253,17 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	{
 		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(l);
 
+		/*
+		 * If the current join commutes with some other outer join(s) via
+		 * outer join identity 3, there will be multiple clones of its join
+		 * clauses in the joininfo list.  We want to consider only the
+		 * has_clone form of such clauses.  Processing more than one form
+		 * would be wasteful, and also some of the others would confuse the
+		 * RINFO_IS_PUSHED_DOWN test below.
+		 */
+		if (restrictinfo->is_clone)
+			continue;			/* ignore it */
+
 		/*
 		 * If it's not a join clause for this outer join, we can't use it.
 		 * Note that if the clause is pushed-down, then it is logically from
@@ -306,10 +323,12 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
  * no longer treated as a baserel, and that attributes of other baserels
  * are no longer marked as being needed at joins involving this rel.
  * Also, join quals involving the rel have to be removed from the joininfo
- * lists, but only if they belong to the outer join identified by joinrelids.
+ * lists, but only if they belong to the outer join identified by ojrelid
+ * and joinrelids.
  */
 static void
-remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
+remove_rel_from_query(PlannerInfo *root, int relid, int ojrelid,
+					  Relids joinrelids)
 {
 	RelOptInfo *rel = find_base_rel(root, relid);
 	List	   *joininfos;
@@ -346,6 +365,8 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 		{
 			otherrel->attr_needed[attroff] =
 				bms_del_member(otherrel->attr_needed[attroff], relid);
+			otherrel->attr_needed[attroff] =
+				bms_del_member(otherrel->attr_needed[attroff], ojrelid);
 		}
 	}
 
@@ -353,6 +374,9 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 	 * Update all_baserels and related relid sets.
 	 */
 	root->all_baserels = bms_del_member(root->all_baserels, relid);
+	root->outer_join_rels = bms_del_member(root->outer_join_rels, ojrelid);
+	root->all_query_rels = bms_del_member(root->all_query_rels, relid);
+	root->all_query_rels = bms_del_member(root->all_query_rels, ojrelid);
 
 	/*
 	 * Likewise remove references from SpecialJoinInfo data structures.
@@ -370,6 +394,14 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 		sjinfo->min_righthand = bms_del_member(sjinfo->min_righthand, relid);
 		sjinfo->syn_lefthand = bms_del_member(sjinfo->syn_lefthand, relid);
 		sjinfo->syn_righthand = bms_del_member(sjinfo->syn_righthand, relid);
+		sjinfo->min_lefthand = bms_del_member(sjinfo->min_lefthand, ojrelid);
+		sjinfo->min_righthand = bms_del_member(sjinfo->min_righthand, ojrelid);
+		sjinfo->syn_lefthand = bms_del_member(sjinfo->syn_lefthand, ojrelid);
+		sjinfo->syn_righthand = bms_del_member(sjinfo->syn_righthand, ojrelid);
+		/* relid cannot appear in these fields, but ojrelid can: */
+		sjinfo->commute_above_l = bms_del_member(sjinfo->commute_above_l, ojrelid);
+		sjinfo->commute_above_r = bms_del_member(sjinfo->commute_above_r, ojrelid);
+		sjinfo->commute_below = bms_del_member(sjinfo->commute_below, ojrelid);
 	}
 
 	/*
@@ -401,8 +433,10 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 		else
 		{
 			phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, relid);
+			phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, ojrelid);
 			Assert(!bms_is_empty(phinfo->ph_eval_at));
 			phinfo->ph_needed = bms_del_member(phinfo->ph_needed, relid);
+			phinfo->ph_needed = bms_del_member(phinfo->ph_needed, ojrelid);
 		}
 	}
 
@@ -427,7 +461,12 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 
 		remove_join_clause_from_rels(root, rinfo, rinfo->required_relids);
 
-		if (RINFO_IS_PUSHED_DOWN(rinfo, joinrelids))
+		/*
+		 * If the qual lists ojrelid in its required_relids, it must have come
+		 * from above the outer join we're removing (so we need to keep it);
+		 * if it does not, then it didn't and we can discard it.
+		 */
+		if (bms_is_member(ojrelid, rinfo->required_relids))
 		{
 			/* Recheck that qual doesn't actually reference the target rel */
 			Assert(!bms_is_member(relid, rinfo->clause_relids));
@@ -439,6 +478,8 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
 			rinfo->required_relids = bms_copy(rinfo->required_relids);
 			rinfo->required_relids = bms_del_member(rinfo->required_relids,
 													relid);
+			rinfo->required_relids = bms_del_member(rinfo->required_relids,
+													ojrelid);
 			distribute_restrictinfo_to_rels(root, rinfo);
 		}
 	}
@@ -553,6 +594,7 @@ reduce_unique_semijoins(PlannerInfo *root)
 
 		/* Compute the relid set for the join we are considering */
 		joinrelids = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+		Assert(sjinfo->ojrelid == 0);	/* SEMI joins don't have RT indexes */
 
 		/*
 		 * Since we're only considering a single-rel RHS, any join clauses it
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 4acbd3df32..7bd654a77e 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -48,7 +48,9 @@ int			join_collapse_limit;
  *
  * deconstruct_recurse recursively examines the join tree and builds a List
  * (in depth-first traversal order) of JoinTreeItem structs, which are then
- * processed iteratively by deconstruct_distribute.
+ * processed iteratively by deconstruct_distribute.  If there are outer
+ * joins, non-degenerate outer join clauses are processed in a third pass
+ * deconstruct_distribute_oj_quals.
  *
  * The JoinTreeItem structs themselves can be freed at the end of
  * deconstruct_jointree, but do not modify or free their substructure,
@@ -60,17 +62,18 @@ typedef struct JoinTreeItem
 	/* Fields filled during deconstruct_recurse: */
 	Node	   *jtnode;			/* jointree node to examine */
 	bool		below_outer_join;	/* is it below an outer join? */
-	Relids		qualscope;		/* base Relids syntactically included in this
-								 * jointree node */
-	Relids		inner_join_rels;	/* base Relids syntactically included in
-									 * inner joins appearing at or below this
-									 * jointree node */
+	Relids		qualscope;		/* base+OJ Relids syntactically included in
+								 * this jointree node */
+	Relids		inner_join_rels;	/* base+OJ Relids syntactically included
+									 * in inner joins appearing at or below
+									 * this jointree node */
 	Relids		left_rels;		/* if join node, Relids of the left side */
 	Relids		right_rels;		/* if join node, Relids of the right side */
 	Relids		nonnullable_rels;	/* if outer join, Relids of the
 									 * non-nullable side */
 	/* Fields filled during deconstruct_distribute: */
 	SpecialJoinInfo *sjinfo;	/* if outer join, its SpecialJoinInfo */
+	List	   *oj_joinclauses; /* outer join quals not yet distributed */
 } JoinTreeItem;
 
 /* Elements of the postponed_qual_list used during deconstruct_distribute */
@@ -94,9 +97,13 @@ static void process_security_barrier_quals(PlannerInfo *root,
 static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
 										   Relids left_rels, Relids right_rels,
 										   Relids inner_join_rels,
-										   JoinType jointype, List *clause);
+										   JoinType jointype, Index ojrelid,
+										   List *clause);
 static void compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo,
 								  List *clause);
+static void deconstruct_distribute_oj_quals(PlannerInfo *root,
+											List *jtitems,
+											JoinTreeItem *jtitem);
 static void distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 									 bool below_outer_join,
 									 SpecialJoinInfo *sjinfo,
@@ -104,7 +111,11 @@ static void distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 									 Relids qualscope,
 									 Relids ojscope,
 									 Relids outerjoin_nonnullable,
-									 List **postponed_qual_list);
+									 bool allow_equivalence,
+									 bool has_clone,
+									 bool is_clone,
+									 List **postponed_qual_list,
+									 List **postponed_oj_qual_list);
 static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									bool below_outer_join,
 									SpecialJoinInfo *sjinfo,
@@ -112,7 +123,11 @@ static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									Relids qualscope,
 									Relids ojscope,
 									Relids outerjoin_nonnullable,
-									List **postponed_qual_list);
+									bool allow_equivalence,
+									bool has_clone,
+									bool is_clone,
+									List **postponed_qual_list,
+									List **postponed_oj_qual_list);
 static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
 								  Relids *nullable_relids_p, bool is_pushed_down);
 static bool check_equivalence_delay(PlannerInfo *root,
@@ -290,10 +305,16 @@ add_vars_to_targetlist(PlannerInfo *root, List *vars,
 			attno -= rel->min_attr;
 			if (rel->attr_needed[attno] == NULL)
 			{
-				/* Variable not yet requested, so add to rel's targetlist */
-				/* XXX is copyObject necessary here? */
-				rel->reltarget->exprs = lappend(rel->reltarget->exprs,
-												copyObject(var));
+				/*
+				 * Variable not yet requested, so add to rel's targetlist.
+				 *
+				 * The value available at the rel's scan level has not been
+				 * nulled by any outer join, so drop its varnullingrels.
+				 * (We'll put those back as we climb up the join tree.)
+				 */
+				var = copyObject(var);
+				var->varnullingrels = NULL;
+				rel->reltarget->exprs = lappend(rel->reltarget->exprs, var);
 				/* reltarget cost and width will be computed later */
 			}
 			rel->attr_needed[attno] = bms_add_members(rel->attr_needed[attno],
@@ -589,8 +610,10 @@ create_lateral_join_info(PlannerInfo *root)
 			varno = -1;
 			while ((varno = bms_next_member(eval_at, varno)) >= 0)
 			{
-				RelOptInfo *brel = find_base_rel(root, varno);
+				RelOptInfo *brel = find_base_rel_ignore_join(root, varno);
 
+				if (brel == NULL)
+					continue;	/* ignore outer joins in eval_at */
 				brel->lateral_relids = bms_add_members(brel->lateral_relids,
 													   phinfo->ph_lateral);
 			}
@@ -681,7 +704,10 @@ create_lateral_join_info(PlannerInfo *root)
 		{
 			RelOptInfo *brel2 = root->simple_rel_array[rti2];
 
-			Assert(brel2 != NULL && brel2->reloptkind == RELOPT_BASEREL);
+			if (brel2 == NULL)
+				continue;		/* must be an OJ */
+
+			Assert(brel2->reloptkind == RELOPT_BASEREL);
 			brel2->lateral_referencers =
 				bms_add_member(brel2->lateral_referencers, rti);
 		}
@@ -743,6 +769,7 @@ deconstruct_jointree(PlannerInfo *root)
 
 	/* These are filled as we scan the jointree */
 	root->all_baserels = NULL;
+	root->outer_join_rels = NULL;
 	root->nullable_baserels = NULL;
 
 	/* Perform the initial scan of the jointree */
@@ -750,6 +777,9 @@ deconstruct_jointree(PlannerInfo *root)
 								 false,
 								 &item_list);
 
+	/* Now we can form the value of all_query_rels, too */
+	root->all_query_rels = bms_union(root->all_baserels, root->outer_join_rels);
+
 	/* Now scan all the jointree nodes again, and distribute quals */
 	foreach(lc, item_list)
 	{
@@ -762,6 +792,40 @@ deconstruct_jointree(PlannerInfo *root)
 	/* Shouldn't be any leftover postponed quals */
 	Assert(postponed_qual_list == NIL);
 
+	/*
+	 * However, if there were any special joins then we may have some
+	 * postponed LEFT JOIN clauses to deal with.
+	 */
+	if (root->join_info_list)
+	{
+		/*
+		 * XXX hack: when we call distribute_qual_to_rels to process one of
+		 * these clauses, neither the owning SpecialJoinInfo nor any later
+		 * ones can appear in root->join_info_list, else the wrong things will
+		 * happen.  Fake it out by emptying join_info_list and rebuilding it
+		 * as we go. This works because join_info_list is only appended to
+		 * during deconstruct_distribute, so we know we are examining
+		 * SpecialJoinInfos bottom-up, just like the first time.  We can get
+		 * rid of this hack later, after fixing things so that
+		 * distribute_qual_to_rels doesn't have that requirement about
+		 * join_info_list.
+		 */
+		root->join_info_list = NIL;
+
+		foreach(lc, item_list)
+		{
+			JoinTreeItem *jtitem = (JoinTreeItem *) lfirst(lc);
+
+			if (jtitem->oj_joinclauses != NIL)
+				deconstruct_distribute_oj_quals(root, item_list, jtitem);
+
+			/* XXX Rest of hack: rebuild join_info_list as we go */
+			if (jtitem->sjinfo)
+				root->join_info_list = lappend(root->join_info_list,
+											   jtitem->sjinfo);
+		}
+	}
+
 	/* Don't need the JoinTreeItems any more */
 	list_free_deep(item_list);
 
@@ -905,6 +969,14 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				/* Compute qualscope etc */
 				jtitem->qualscope = bms_union(left_item->qualscope,
 											  right_item->qualscope);
+				/* caution: ANTI join derived from SEMI will lack rtindex */
+				if (j->rtindex != 0)
+				{
+					jtitem->qualscope = bms_add_member(jtitem->qualscope,
+													   j->rtindex);
+					root->outer_join_rels = bms_add_member(root->outer_join_rels,
+														   j->rtindex);
+				}
 				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
 													right_item->inner_join_rels);
 				jtitem->left_rels = left_item->qualscope;
@@ -925,6 +997,8 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				/* Compute qualscope etc */
 				jtitem->qualscope = bms_union(left_item->qualscope,
 											  right_item->qualscope);
+				/* SEMI join never has rtindex, so don't add to anything */
+				Assert(j->rtindex == 0);
 				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
 													right_item->inner_join_rels);
 				jtitem->left_rels = left_item->qualscope;
@@ -952,6 +1026,11 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				/* Compute qualscope etc */
 				jtitem->qualscope = bms_union(left_item->qualscope,
 											  right_item->qualscope);
+				Assert(j->rtindex != 0);
+				jtitem->qualscope = bms_add_member(jtitem->qualscope,
+												   j->rtindex);
+				root->outer_join_rels = bms_add_member(root->outer_join_rels,
+													   j->rtindex);
 				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
 													right_item->inner_join_rels);
 				jtitem->left_rels = left_item->qualscope;
@@ -1073,7 +1152,8 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 										NULL,
 										root->qual_security_level,
 										jtitem->qualscope, NULL, NULL,
-										NULL);
+										true, false, false,
+										NULL, NULL);
 			else
 				new_postponed_quals = lappend(new_postponed_quals, pq);
 		}
@@ -1087,7 +1167,8 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 								 NULL,
 								 root->qual_security_level,
 								 jtitem->qualscope, NULL, NULL,
-								 postponed_qual_list);
+								 true, false, false,
+								 postponed_qual_list, NULL);
 	}
 	else if (IsA(jtnode, JoinExpr))
 	{
@@ -1096,6 +1177,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 		Relids		ojscope;
 		List	   *my_quals;
 		SpecialJoinInfo *sjinfo;
+		List	  **postponed_oj_qual_list;
 		ListCell   *l;
 
 		/*
@@ -1138,6 +1220,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 										jtitem->right_rels,
 										jtitem->inner_join_rels,
 										j->jointype,
+										j->rtindex,
 										my_quals);
 			jtitem->sjinfo = sjinfo;
 			if (j->jointype == JOIN_SEMI)
@@ -1146,6 +1229,19 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 			{
 				ojscope = bms_union(sjinfo->min_lefthand,
 									sjinfo->min_righthand);
+
+				/*
+				 * Add back any commutable lower OJ relids that were removed
+				 * from min_lefthand or min_righthand, else the ojscope
+				 * cross-check in distribute_qual_to_rels will complain.  If
+				 * any such OJs were removed, we will postpone processing of
+				 * non-degenerate clauses, so this addition doesn't affect
+				 * anything except that cross-check and some Asserts.  Real
+				 * clause positioning decisions will be made later, when we
+				 * revisit the postponed clauses.
+				 */
+				if (sjinfo->commute_below)
+					ojscope = bms_add_members(ojscope, sjinfo->commute_below);
 			}
 		}
 		else
@@ -1154,6 +1250,18 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 			ojscope = NULL;
 		}
 
+		/*
+		 * If it's a left join with a join clause that is strict for the LHS,
+		 * then we need to postpone handling of any non-degenerate join
+		 * clauses, in case the join is able to commute with another left join
+		 * per identity 3.  (Degenerate clauses need not be postponed, since
+		 * they will drop down below this join anyway.)
+		 */
+		if (j->jointype == JOIN_LEFT && sjinfo->lhs_strict)
+			postponed_oj_qual_list = &jtitem->oj_joinclauses;
+		else
+			postponed_oj_qual_list = NULL;
+
 		/* Process the JOIN's qual clauses */
 		distribute_quals_to_rels(root, my_quals,
 								 jtitem->below_outer_join,
@@ -1161,7 +1269,10 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 								 root->qual_security_level,
 								 jtitem->qualscope,
 								 ojscope, jtitem->nonnullable_rels,
-								 postponed_qual_list);
+								 true,	/* allow_equivalence */
+								 false, false,	/* not clones */
+								 postponed_qual_list,
+								 postponed_oj_qual_list);
 
 		/* And add the SpecialJoinInfo to join_info_list */
 		if (sjinfo)
@@ -1223,6 +1334,9 @@ process_security_barrier_quals(PlannerInfo *root,
 								 qualscope,
 								 qualscope,
 								 NULL,
+								 true,
+								 false, false,	/* not clones */
+								 NULL,
 								 NULL);
 		security_level++;
 	}
@@ -1236,10 +1350,11 @@ process_security_barrier_quals(PlannerInfo *root,
  *	  Build a SpecialJoinInfo for the current outer join
  *
  * Inputs:
- *	left_rels: the base Relids syntactically on outer side of join
- *	right_rels: the base Relids syntactically on inner side of join
- *	inner_join_rels: base Relids participating in inner joins below this one
+ *	left_rels: the base+OJ Relids syntactically on outer side of join
+ *	right_rels: the base+OJ Relids syntactically on inner side of join
+ *	inner_join_rels: base+OJ Relids participating in inner joins below this one
  *	jointype: what it says (must always be LEFT, FULL, SEMI, or ANTI)
+ *	ojrelid: RT index of the join RTE (0 for SEMI, which isn't in the RT list)
  *	clause: the outer join's join condition (in implicit-AND format)
  *
  * The node should eventually be appended to root->join_info_list, but we
@@ -1253,7 +1368,8 @@ static SpecialJoinInfo *
 make_outerjoininfo(PlannerInfo *root,
 				   Relids left_rels, Relids right_rels,
 				   Relids inner_join_rels,
-				   JoinType jointype, List *clause)
+				   JoinType jointype, Index ojrelid,
+				   List *clause)
 {
 	SpecialJoinInfo *sjinfo = makeNode(SpecialJoinInfo);
 	Relids		clause_relids;
@@ -1301,6 +1417,11 @@ make_outerjoininfo(PlannerInfo *root,
 	sjinfo->syn_lefthand = left_rels;
 	sjinfo->syn_righthand = right_rels;
 	sjinfo->jointype = jointype;
+	sjinfo->ojrelid = ojrelid;
+	/* these fields may get added to later: */
+	sjinfo->commute_above_l = NULL;
+	sjinfo->commute_above_r = NULL;
+	sjinfo->commute_below = NULL;
 	/* this always starts out false */
 	sjinfo->delay_upper_joins = false;
 
@@ -1348,6 +1469,7 @@ make_outerjoininfo(PlannerInfo *root,
 	foreach(l, root->join_info_list)
 	{
 		SpecialJoinInfo *otherinfo = (SpecialJoinInfo *) lfirst(l);
+		bool		have_unsafe_phvs;
 
 		/*
 		 * A full join is an optimization barrier: we can't associate into or
@@ -1363,6 +1485,9 @@ make_outerjoininfo(PlannerInfo *root,
 											   otherinfo->syn_lefthand);
 				min_lefthand = bms_add_members(min_lefthand,
 											   otherinfo->syn_righthand);
+				if (otherinfo->ojrelid != 0)
+					min_lefthand = bms_add_member(min_lefthand,
+												  otherinfo->ojrelid);
 			}
 			if (bms_overlap(right_rels, otherinfo->syn_lefthand) ||
 				bms_overlap(right_rels, otherinfo->syn_righthand))
@@ -1371,11 +1496,26 @@ make_outerjoininfo(PlannerInfo *root,
 												otherinfo->syn_lefthand);
 				min_righthand = bms_add_members(min_righthand,
 												otherinfo->syn_righthand);
+				if (otherinfo->ojrelid != 0)
+					min_righthand = bms_add_member(min_righthand,
+												   otherinfo->ojrelid);
 			}
 			/* Needn't do anything else with the full join */
 			continue;
 		}
 
+		/*
+		 * If our join condition contains any PlaceHolderVars that need to be
+		 * evaluated above the lower OJ, then we can't commute with it.
+		 */
+		if (otherinfo->ojrelid != 0)
+			have_unsafe_phvs =
+				contain_placeholder_references_to(root,
+												  (Node *) clause,
+												  otherinfo->ojrelid);
+		else
+			have_unsafe_phvs = false;
+
 		/*
 		 * For a lower OJ in our LHS, if our join condition uses the lower
 		 * join's RHS and is not strict for that rel, we must preserve the
@@ -1383,23 +1523,44 @@ make_outerjoininfo(PlannerInfo *root,
 		 * min_lefthand.  (We must use its full syntactic relset, not just its
 		 * min_lefthand + min_righthand.  This is because there might be other
 		 * OJs below this one that this one can commute with, but we cannot
-		 * commute with them if we don't with this one.)  Also, if the current
-		 * join is a semijoin or antijoin, we must preserve ordering
-		 * regardless of strictness.
+		 * commute with them if we don't with this one.)  Also, if we have
+		 * unsafe PHVs or the current join is a semijoin or antijoin, we must
+		 * preserve ordering regardless of strictness.
 		 *
 		 * Note: I believe we have to insist on being strict for at least one
 		 * rel in the lower OJ's min_righthand, not its whole syn_righthand.
+		 *
+		 * When we don't need to preserve ordering, check to see if outer join
+		 * identity 3 applies, and if so, remove the lower OJ's ojrelid from
+		 * our min_lefthand so that commutation is allowed.
 		 */
 		if (bms_overlap(left_rels, otherinfo->syn_righthand))
 		{
 			if (bms_overlap(clause_relids, otherinfo->syn_righthand) &&
-				(jointype == JOIN_SEMI || jointype == JOIN_ANTI ||
+				(have_unsafe_phvs ||
+				 jointype == JOIN_SEMI || jointype == JOIN_ANTI ||
 				 !bms_overlap(strict_relids, otherinfo->min_righthand)))
 			{
+				/* Preserve ordering */
 				min_lefthand = bms_add_members(min_lefthand,
 											   otherinfo->syn_lefthand);
 				min_lefthand = bms_add_members(min_lefthand,
 											   otherinfo->syn_righthand);
+				if (otherinfo->ojrelid != 0)
+					min_lefthand = bms_add_member(min_lefthand,
+												  otherinfo->ojrelid);
+			}
+			else if (jointype == JOIN_LEFT &&
+					 otherinfo->jointype == JOIN_LEFT &&
+					 bms_overlap(strict_relids, otherinfo->min_righthand))
+			{
+				/* Identity 3 applies, so remove the ordering restriction */
+				min_lefthand = bms_del_member(min_lefthand, otherinfo->ojrelid);
+				/* Add commutability markers to both SpecialJoinInfos */
+				otherinfo->commute_above_l =
+					bms_add_member(otherinfo->commute_above_l, ojrelid);
+				sjinfo->commute_below =
+					bms_add_member(sjinfo->commute_below, otherinfo->ojrelid);
 			}
 		}
 
@@ -1414,8 +1575,8 @@ make_outerjoininfo(PlannerInfo *root,
 		 * up with SpecialJoinInfos with identical min_righthands, which can
 		 * confuse join_is_legal (see discussion in backend/optimizer/README).
 		 *
-		 * Also, we must preserve ordering anyway if either the current join
-		 * or the lower OJ is either a semijoin or an antijoin.
+		 * Also, we must preserve ordering anyway if we have unsafe PHVs, or
+		 * if either this join or the lower OJ is a semijoin or antijoin.
 		 *
 		 * Here, we have to consider that "our join condition" includes any
 		 * clauses that syntactically appeared above the lower OJ and below
@@ -1427,21 +1588,43 @@ make_outerjoininfo(PlannerInfo *root,
 		 * join condition are not affected by them.  The net effect is
 		 * therefore sufficiently represented by the delay_upper_joins flag
 		 * saved for us by check_outerjoin_delay.
+		 *
+		 * When we don't need to preserve ordering, check to see if outer join
+		 * identity 3 applies, and if so, remove the lower OJ's ojrelid from
+		 * our min_righthand so that commutation is allowed.
 		 */
 		if (bms_overlap(right_rels, otherinfo->syn_righthand))
 		{
 			if (bms_overlap(clause_relids, otherinfo->syn_righthand) ||
 				!bms_overlap(clause_relids, otherinfo->min_lefthand) ||
+				have_unsafe_phvs ||
 				jointype == JOIN_SEMI ||
 				jointype == JOIN_ANTI ||
 				otherinfo->jointype == JOIN_SEMI ||
 				otherinfo->jointype == JOIN_ANTI ||
 				!otherinfo->lhs_strict || otherinfo->delay_upper_joins)
 			{
+				/* Preserve ordering */
 				min_righthand = bms_add_members(min_righthand,
 												otherinfo->syn_lefthand);
 				min_righthand = bms_add_members(min_righthand,
 												otherinfo->syn_righthand);
+				if (otherinfo->ojrelid != 0)
+					min_righthand = bms_add_member(min_righthand,
+												   otherinfo->ojrelid);
+			}
+			else if (jointype == JOIN_LEFT &&
+					 otherinfo->jointype == JOIN_LEFT &&
+					 otherinfo->lhs_strict)
+			{
+				/* Identity 3 applies, so remove the ordering restriction */
+				min_righthand = bms_del_member(min_righthand,
+											   otherinfo->ojrelid);
+				/* Add commutability markers to both SpecialJoinInfos */
+				otherinfo->commute_above_r =
+					bms_add_member(otherinfo->commute_above_r, ojrelid);
+				sjinfo->commute_below =
+					bms_add_member(sjinfo->commute_below, otherinfo->ojrelid);
 			}
 		}
 	}
@@ -1666,6 +1849,207 @@ compute_semijoin_info(PlannerInfo *root, SpecialJoinInfo *sjinfo, List *clause)
 	sjinfo->semi_rhs_exprs = semi_rhs_exprs;
 }
 
+/*
+ * deconstruct_distribute_oj_quals
+ *	  Adjust LEFT JOIN quals to be suitable for commuted-left-join cases,
+ *	  then push them into the joinqual lists and EquivalenceClass structures.
+ *
+ * This runs immediately after we've completed the deconstruct_distribute scan.
+ * jtitems contains all the JoinTreeItems (in depth-first order), and jtitem
+ * is one that has postponed oj_joinclauses to deal with.
+ */
+static void
+deconstruct_distribute_oj_quals(PlannerInfo *root,
+								List *jtitems,
+								JoinTreeItem *jtitem)
+{
+	SpecialJoinInfo *sjinfo = jtitem->sjinfo;
+	Relids		qualscope,
+				ojscope,
+				nonnullable_rels;
+
+	/* Recompute syntactic and semantic scopes of this left join */
+	qualscope = bms_union(sjinfo->syn_lefthand, sjinfo->syn_righthand);
+	qualscope = bms_add_member(qualscope, sjinfo->ojrelid);
+	ojscope = bms_union(sjinfo->min_lefthand, sjinfo->min_righthand);
+	nonnullable_rels = sjinfo->syn_lefthand;
+
+	/*
+	 * If this join can commute with any other ones per outer-join identity 3,
+	 * and it is the one providing the join clause with flexible semantics,
+	 * then we have to generate variants of the join clause with different
+	 * nullingrels labeling.  Otherwise, just push out the postponed clause
+	 * as-is.
+	 */
+	Assert(sjinfo->lhs_strict); /* else we shouldn't be here */
+	if (sjinfo->commute_above_r ||
+		bms_overlap(sjinfo->commute_below, sjinfo->syn_lefthand))
+	{
+		Relids		joins_above;
+		Relids		joins_below;
+		Relids		joins_so_far;
+		List	   *quals;
+		ListCell   *lc;
+
+		/*
+		 * Put any OJ relids that were removed from min_righthand back into
+		 * ojscope, else distribute_qual_to_rels will complain.
+		 */
+		ojscope = bms_join(ojscope, bms_intersect(sjinfo->commute_below,
+												  sjinfo->syn_righthand));
+
+		/* Identify the outer joins this one commutes with */
+		joins_above = sjinfo->commute_above_r;
+		joins_below = bms_intersect(sjinfo->commute_below,
+									sjinfo->syn_lefthand);
+
+		/*
+		 * Generate qual variants with different sets of nullingrels bits.
+		 *
+		 * We only need bit-sets that correspond to the successively less
+		 * deeply syntactically-nested subsets of this join and its
+		 * commutators.  That's true first because obviously only those forms
+		 * of the Vars and PHVs could appear elsewhere in the query, and
+		 * second because the outer join identities do not provide a way to
+		 * re-order such joins in a way that would require different marking.
+		 * (That is, while the current join may commute with several others,
+		 * none of those others can commute with each other.)  To visit the
+		 * interesting joins in syntactic nesting order, we rely on the
+		 * jtitems list to be ordered that way.
+		 *
+		 * We first strip out all the nullingrels bits corresponding to
+		 * commutating joins below this one, and then successively put them
+		 * back as we crawl up the join stack.
+		 */
+		quals = jtitem->oj_joinclauses;
+		if (!bms_is_empty(joins_below))
+			quals = (List *) remove_nulling_relids((Node *) quals,
+												   joins_below,
+												   NULL);
+
+		joins_so_far = NULL;
+		foreach(lc, jtitems)
+		{
+			JoinTreeItem *otherjtitem = (JoinTreeItem *) lfirst(lc);
+			SpecialJoinInfo *othersj = otherjtitem->sjinfo;
+			bool		below_sjinfo = false;
+			bool		above_sjinfo = false;
+			Relids		this_qualscope;
+			Relids		this_ojscope;
+			bool		allow_equivalence,
+						has_clone,
+						is_clone;
+
+			if (othersj == NULL)
+				continue;		/* not an outer-join item, ignore */
+
+			if (bms_is_member(othersj->ojrelid, joins_below))
+			{
+				/* othersj commutes with sjinfo from below left */
+				below_sjinfo = true;
+			}
+			else if (othersj == sjinfo)
+			{
+				/* found our join in syntactic order */
+				Assert(bms_equal(joins_so_far, joins_below));
+			}
+			else if (bms_is_member(othersj->ojrelid, joins_above))
+			{
+				/* othersj commutes with sjinfo from above */
+				above_sjinfo = true;
+			}
+			else
+			{
+				/* othersj is not relevant, ignore */
+				continue;
+			}
+
+			/*
+			 * When we are looking at joins above sjinfo, we are envisioning
+			 * pushing sjinfo to above othersj, so add othersj's nulling bit
+			 * before distributing the quals.
+			 */
+			if (above_sjinfo)
+				quals = (List *)
+					add_nulling_relids((Node *) quals,
+									   othersj->min_righthand,
+									   bms_make_singleton(othersj->ojrelid));
+
+			/* Compute qualscope and ojscope for this join level */
+			this_qualscope = bms_union(qualscope, joins_so_far);
+			this_ojscope = bms_union(ojscope, joins_so_far);
+			if (above_sjinfo)
+			{
+				/* othersj is not yet in joins_so_far, but we need it */
+				this_qualscope = bms_add_member(this_qualscope,
+												othersj->ojrelid);
+				this_ojscope = bms_add_member(this_ojscope,
+											  othersj->ojrelid);
+				/* sjinfo is in joins_so_far, and we don't want it */
+				this_ojscope = bms_del_member(this_ojscope,
+											  sjinfo->ojrelid);
+			}
+
+			/*
+			 * We generate EquivalenceClasses only from the first form of the
+			 * quals, with the fewest nullingrels bits set.  An EC made from
+			 * this version of the quals can be useful below the outer-join
+			 * nest, whereas versions with some nullingrels bits set would not
+			 * be.  We cannot generate ECs from more than one version, or
+			 * we'll make nonsensical conclusions that Vars with nullingrels
+			 * bits set are equal to their versions without.  Fortunately,
+			 * such ECs wouldn't be very useful anyway, because they'd equate
+			 * values not observable outside the join nest.  (See
+			 * optimizer/README.)
+			 *
+			 * The first form of the quals is also the only one marked as
+			 * has_clone rather than is_clone.
+			 */
+			allow_equivalence = (joins_so_far == NULL);
+			has_clone = allow_equivalence;
+			is_clone = !has_clone;
+
+			distribute_quals_to_rels(root, quals,
+									 true,
+									 sjinfo,
+									 root->qual_security_level,
+									 this_qualscope,
+									 this_ojscope, nonnullable_rels,
+									 allow_equivalence,
+									 has_clone,
+									 is_clone,
+									 NULL, NULL);	/* no more postponement */
+
+			/*
+			 * Adjust qual nulling bits for next level up, if needed.  We
+			 * don't want to put sjinfo's own bit in at all, and if we're
+			 * above sjinfo then we did it already.
+			 */
+			if (below_sjinfo)
+				quals = (List *)
+					add_nulling_relids((Node *) quals,
+									   othersj->min_righthand,
+									   bms_make_singleton(othersj->ojrelid));
+
+			/* ... and track joins processed so far */
+			joins_so_far = bms_add_member(joins_so_far, othersj->ojrelid);
+		}
+	}
+	else
+	{
+		/* No commutation possible, just process the postponed clauses */
+		distribute_quals_to_rels(root, jtitem->oj_joinclauses,
+								 true,
+								 sjinfo,
+								 root->qual_security_level,
+								 qualscope,
+								 ojscope, nonnullable_rels,
+								 true,	/* allow_equivalence */
+								 false, false,	/* not clones */
+								 NULL, NULL);	/* no more postponement */
+	}
+}
+
 
 /*****************************************************************************
  *
@@ -1686,7 +2070,11 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 						 Relids qualscope,
 						 Relids ojscope,
 						 Relids outerjoin_nonnullable,
-						 List **postponed_qual_list)
+						 bool allow_equivalence,
+						 bool has_clone,
+						 bool is_clone,
+						 List **postponed_qual_list,
+						 List **postponed_oj_qual_list)
 {
 	ListCell   *lc;
 
@@ -1701,7 +2089,11 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 								qualscope,
 								ojscope,
 								outerjoin_nonnullable,
-								postponed_qual_list);
+								allow_equivalence,
+								has_clone,
+								is_clone,
+								postponed_qual_list,
+								postponed_oj_qual_list);
 	}
 }
 
@@ -1711,26 +2103,35 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
  *	  (depending on whether the clause is a join) of each base relation
  *	  mentioned in the clause.  A RestrictInfo node is created and added to
  *	  the appropriate list for each rel.  Alternatively, if the clause uses a
- *	  mergejoinable operator and is not delayed by outer-join rules, enter
- *	  the left- and right-side expressions into the query's list of
- *	  EquivalenceClasses.  Alternatively, if the clause needs to be treated
- *	  as belonging to a higher join level, just add it to postponed_qual_list.
+ *	  mergejoinable operator, enter its left- and right-side expressions into
+ *	  the query's EquivalenceClasses.
+ *
+ * In some cases, quals will be added to postponed_qual_list or
+ * postponed_oj_qual_list instead of being processed right away.
+ * These will be dealt with in later steps of deconstruct_jointree.
  *
  * 'clause': the qual clause to be distributed
  * 'below_outer_join': true if the qual is from a JOIN/ON that is below the
  *		nullable side of a higher-level outer join
  * 'sjinfo': join's SpecialJoinInfo (NULL for an inner join or WHERE clause)
  * 'security_level': security_level to assign to the qual
- * 'qualscope': set of baserels the qual's syntactic scope covers
- * 'ojscope': NULL if not an outer-join qual, else the minimum set of baserels
- *		needed to form this join
+ * 'qualscope': set of base+OJ rels the qual's syntactic scope covers
+ * 'ojscope': NULL if not an outer-join qual, else the minimum set of base+OJ
+ *		rels needed to form this join
  * 'outerjoin_nonnullable': NULL if not an outer-join qual, else the set of
- *		baserels appearing on the outer (nonnullable) side of the join
+ *		base+OJ rels appearing on the outer (nonnullable) side of the join
  *		(for FULL JOIN this includes both sides of the join, and must in fact
  *		equal qualscope)
+ * 'allow_equivalence': true if it's okay to convert clause into an
+ *		EquivalenceClass
+ * 'has_clone': has_clone property to assign to the qual
+ * 'is_clone': is_clone property to assign to the qual
  * 'postponed_qual_list': list of PostponedQual structs, which we can add
  *		this qual to if it turns out to belong to a higher join level.
  *		Can be NULL if caller knows postponement is impossible.
+ * 'postponed_oj_qual_list': if not NULL, non-degenerate outer join clauses
+ *		should be added to this list instead of being processed (list entries
+ *		are just the bare clauses)
  *
  * 'qualscope' identifies what level of JOIN the qual came from syntactically.
  * 'ojscope' is needed if we decide to force the qual up to the outer-join
@@ -1748,7 +2149,11 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 						Relids qualscope,
 						Relids ojscope,
 						Relids outerjoin_nonnullable,
-						List **postponed_qual_list)
+						bool allow_equivalence,
+						bool has_clone,
+						bool is_clone,
+						List **postponed_qual_list,
+						List **postponed_oj_qual_list)
 {
 	Relids		relids;
 	bool		is_pushed_down;
@@ -1842,7 +2247,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 				{
 					relids =
 						get_relids_in_jointree((Node *) root->parse->jointree,
-											   false);
+											   true, false);
 					qualscope = bms_copy(relids);
 				}
 			}
@@ -1885,8 +2290,18 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	{
 		/*
 		 * The qual is attached to an outer join and mentions (some of the)
-		 * rels on the nonnullable side, so it's not degenerate.
-		 *
+		 * rels on the nonnullable side, so it's not degenerate.  If the
+		 * caller wants to postpone handling such clauses, just add it to
+		 * postponed_oj_qual_list and return.  (The work we've done up to here
+		 * will have to be redone later, but there's not much of it.)
+		 */
+		if (postponed_oj_qual_list != NULL)
+		{
+			*postponed_oj_qual_list = lappend(*postponed_oj_qual_list, clause);
+			return;
+		}
+
+		/*
 		 * We can't use such a clause to deduce equivalence (the left and
 		 * right sides might be unequal above the join because one of them has
 		 * gone to NULL) ... but we might be able to use it for more limited
@@ -1952,6 +2367,11 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 			if (check_redundant_nullability_qual(root, clause))
 				return;
 		}
+		else if (!allow_equivalence)
+		{
+			/* Caller says it mustn't become an equivalence class */
+			maybe_equivalence = false;
+		}
 		else
 		{
 			/*
@@ -1986,11 +2406,22 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									 outerjoin_nonnullable,
 									 nullable_relids);
 
+	/* Apply appropriate clone marking, too */
+	restrictinfo->has_clone = has_clone;
+	restrictinfo->is_clone = is_clone;
+
 	/*
-	 * If it's a join clause (either naturally, or because delayed by
-	 * outer-join rules), add vars used in the clause to targetlists of their
-	 * relations, so that they will be emitted by the plan nodes that scan
-	 * those relations (else they won't be available at the join node!).
+	 * If it's a join clause, add vars used in the clause to targetlists of
+	 * their relations, so that they will be emitted by the plan nodes that
+	 * scan those relations (else they won't be available at the join node!).
+	 *
+	 * Normally we mark the vars as needed at the join identified by "relids".
+	 * However, if this is a clone clause then ignore the outer-join relids in
+	 * that set.  Otherwise, vars appearing in a cloned clause would end up
+	 * marked as having to propagate to the highest one of the commuting
+	 * joins, which would often be an overestimate.  For such clauses, correct
+	 * var propagation is ensured by making ojscope include input rels from
+	 * both sides of the join.
 	 *
 	 * Note: if the clause gets absorbed into an EquivalenceClass then this
 	 * may be unnecessary, but for now we have to do it to cover the case
@@ -2003,8 +2434,13 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 										   PVC_RECURSE_AGGREGATES |
 										   PVC_RECURSE_WINDOWFUNCS |
 										   PVC_INCLUDE_PLACEHOLDERS);
+		Relids		where_needed;
 
-		add_vars_to_targetlist(root, vars, relids);
+		if (is_clone)
+			where_needed = bms_intersect(relids, root->all_baserels);
+		else
+			where_needed = relids;
+		add_vars_to_targetlist(root, vars, where_needed);
 		list_free(vars);
 	}
 
@@ -2495,7 +2931,7 @@ process_implied_equality(PlannerInfo *root,
 			{
 				relids =
 					get_relids_in_jointree((Node *) root->parse->jointree,
-										   false);
+										   true, false);
 			}
 		}
 	}
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 05f44faf6e..8a472bce0c 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -2246,7 +2246,7 @@ preprocess_rowmarks(PlannerInfo *root)
 	 * make a bitmapset of all base rels and then remove the items we don't
 	 * need or have FOR [KEY] UPDATE/SHARE marks for.
 	 */
-	rels = get_relids_in_jointree((Node *) parse->jointree, false);
+	rels = get_relids_in_jointree((Node *) parse->jointree, false, false);
 	if (parse->resultRelation)
 		rels = bms_del_member(rels, parse->resultRelation);
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 85ba9d1ca1..8ea257f492 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -30,11 +30,21 @@
 #include "utils/syscache.h"

+typedef enum
+{
+	NRM_EQUAL,					/* expect exact match of nullingrels */
+	NRM_SUBSET,					/* actual Var may have a subset of input */
+	NRM_SUPERSET				/* actual Var may have a superset of input */
+} NullingRelsMatch;
+
 typedef struct
 {
 	int			varno;			/* RT index of Var */
 	AttrNumber	varattno;		/* attr number of Var */
 	AttrNumber	resno;			/* TLE position of Var */
+#ifdef USE_ASSERT_CHECKING
+	Bitmapset  *varnullingrels; /* Var's varnullingrels */
+#endif
 } tlist_vinfo;
 
 typedef struct
@@ -60,6 +70,7 @@ typedef struct
 	indexed_tlist *inner_itlist;
 	Index		acceptable_rel;
 	int			rtoffset;
+	NullingRelsMatch nrm_match;
 	double		num_exec;
 } fix_join_expr_context;
 
@@ -69,6 +80,7 @@ typedef struct
 	indexed_tlist *subplan_itlist;
 	int			newvarno;
 	int			rtoffset;
+	NullingRelsMatch nrm_match;
 	double		num_exec;
 } fix_upper_expr_context;
 
@@ -159,7 +171,12 @@ static indexed_tlist *build_tlist_index(List *tlist);
 static Var *search_indexed_tlist_for_var(Var *var,
 										 indexed_tlist *itlist,
 										 int newvarno,
-										 int rtoffset);
+										 int rtoffset,
+										 NullingRelsMatch nrm_match);
+static Var *search_indexed_tlist_for_phv(PlaceHolderVar *phv,
+										 indexed_tlist *itlist,
+										 int newvarno,
+										 NullingRelsMatch nrm_match);
 static Var *search_indexed_tlist_for_non_var(Expr *node,
 											 indexed_tlist *itlist,
 											 int newvarno);
@@ -172,14 +189,18 @@ static List *fix_join_expr(PlannerInfo *root,
 						   indexed_tlist *outer_itlist,
 						   indexed_tlist *inner_itlist,
 						   Index acceptable_rel,
-						   int rtoffset, double num_exec);
+						   int rtoffset,
+						   NullingRelsMatch nrm_match,
+						   double num_exec);
 static Node *fix_join_expr_mutator(Node *node,
 								   fix_join_expr_context *context);
 static Node *fix_upper_expr(PlannerInfo *root,
 							Node *node,
 							indexed_tlist *subplan_itlist,
 							int newvarno,
-							int rtoffset, double num_exec);
+							int rtoffset,
+							NullingRelsMatch nrm_match,
+							double num_exec);
 static Node *fix_upper_expr_mutator(Node *node,
 									fix_upper_expr_context *context);
 static List *set_returning_clause_references(PlannerInfo *root,
@@ -1118,13 +1139,13 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 						fix_join_expr(root, splan->onConflictSet,
 									  NULL, itlist,
 									  linitial_int(splan->resultRelations),
-									  rtoffset, NUM_EXEC_QUAL(plan));
+									  rtoffset, NRM_EQUAL, NUM_EXEC_QUAL(plan));
 
 					splan->onConflictWhere = (Node *)
 						fix_join_expr(root, (List *) splan->onConflictWhere,
 									  NULL, itlist,
 									  linitial_int(splan->resultRelations),
-									  rtoffset, NUM_EXEC_QUAL(plan));
+									  rtoffset, NRM_EQUAL, NUM_EXEC_QUAL(plan));
 
 					pfree(itlist);
 
@@ -1181,6 +1202,7 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 															   NULL, itlist,
 															   resultrel,
 															   rtoffset,
+															   NRM_EQUAL,
 															   NUM_EXEC_TLIST(plan));
 
 							/* Fix quals too. */
@@ -1189,6 +1211,7 @@ set_plan_refs(PlannerInfo *root, Plan *plan, int rtoffset)
 																  NULL, itlist,
 																  resultrel,
 																  rtoffset,
+																  NRM_EQUAL,
 																  NUM_EXEC_QUAL(plan));
 						}
 					}
@@ -1334,6 +1357,7 @@ set_indexonlyscan_references(PlannerInfo *root,
 					   index_itlist,
 					   INDEX_VAR,
 					   rtoffset,
+					   NRM_EQUAL,
 					   NUM_EXEC_TLIST((Plan *) plan));
 	plan->scan.plan.qual = (List *)
 		fix_upper_expr(root,
@@ -1341,6 +1365,7 @@ set_indexonlyscan_references(PlannerInfo *root,
 					   index_itlist,
 					   INDEX_VAR,
 					   rtoffset,
+					   NRM_EQUAL,
 					   NUM_EXEC_QUAL((Plan *) plan));
 	plan->recheckqual = (List *)
 		fix_upper_expr(root,
@@ -1348,6 +1373,7 @@ set_indexonlyscan_references(PlannerInfo *root,
 					   index_itlist,
 					   INDEX_VAR,
 					   rtoffset,
+					   NRM_EQUAL,
 					   NUM_EXEC_QUAL((Plan *) plan));
 	/* indexqual is already transformed to reference index columns */
 	plan->indexqual = fix_scan_list(root, plan->indexqual,
@@ -1554,6 +1580,7 @@ set_foreignscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_TLIST((Plan *) fscan));
 		fscan->scan.plan.qual = (List *)
 			fix_upper_expr(root,
@@ -1561,6 +1588,7 @@ set_foreignscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_QUAL((Plan *) fscan));
 		fscan->fdw_exprs = (List *)
 			fix_upper_expr(root,
@@ -1568,6 +1596,7 @@ set_foreignscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_QUAL((Plan *) fscan));
 		fscan->fdw_recheck_quals = (List *)
 			fix_upper_expr(root,
@@ -1575,6 +1604,7 @@ set_foreignscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_QUAL((Plan *) fscan));
 		pfree(itlist);
 		/* fdw_scan_tlist itself just needs fix_scan_list() adjustments */
@@ -1635,6 +1665,7 @@ set_customscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_TLIST((Plan *) cscan));
 		cscan->scan.plan.qual = (List *)
 			fix_upper_expr(root,
@@ -1642,6 +1673,7 @@ set_customscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_QUAL((Plan *) cscan));
 		cscan->custom_exprs = (List *)
 			fix_upper_expr(root,
@@ -1649,6 +1681,7 @@ set_customscan_references(PlannerInfo *root,
 						   itlist,
 						   INDEX_VAR,
 						   rtoffset,
+						   NRM_EQUAL,
 						   NUM_EXEC_QUAL((Plan *) cscan));
 		pfree(itlist);
 		/* custom_scan_tlist itself just needs fix_scan_list() adjustments */
@@ -1835,6 +1868,7 @@ set_hash_references(PlannerInfo *root, Plan *plan, int rtoffset)
 					   outer_itlist,
 					   OUTER_VAR,
 					   rtoffset,
+					   NRM_EQUAL,
 					   NUM_EXEC_QUAL(plan));
 
 	/* Hash doesn't project */
@@ -2170,6 +2204,7 @@ fix_scan_expr_mutator(Node *node, fix_scan_expr_context *context)
 		/* At scan level, we should always just evaluate the contained expr */
 		PlaceHolderVar *phv = (PlaceHolderVar *) node;
 
+		Assert(phv->phnullingrels == NULL);
 		return fix_scan_expr_mutator((Node *) phv->phexpr, context);
 	}
 	if (IsA(node, AlternativeSubPlan))
@@ -2227,6 +2262,7 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 								   inner_itlist,
 								   (Index) 0,
 								   rtoffset,
+								   NRM_EQUAL,
 								   NUM_EXEC_QUAL((Plan *) join));
 
 	/* Now do join-type-specific stuff */
@@ -2239,11 +2275,21 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 		{
 			NestLoopParam *nlp = (NestLoopParam *) lfirst(lc);
 
+			/*
+			 * Because we don't reparameterize parameterized paths to match
+			 * the outer-join level at which they are used, Vars seen in the
+			 * NestLoopParam expression may have nullingrels that are just a
+			 * subset of those in the Vars actually available from the outer
+			 * side.  Not checking this exactly is a bit grotty, but the work
+			 * needed to make things match up perfectly seems well out of
+			 * proportion to the value.
+			 */
 			nlp->paramval = (Var *) fix_upper_expr(root,
 												   (Node *) nlp->paramval,
 												   outer_itlist,
 												   OUTER_VAR,
 												   rtoffset,
+												   NRM_SUBSET,
 												   NUM_EXEC_TLIST(outer_plan));
 			/* Check we replaced any PlaceHolderVar with simple Var */
 			if (!(IsA(nlp->paramval, Var) &&
@@ -2261,6 +2307,7 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 										 inner_itlist,
 										 (Index) 0,
 										 rtoffset,
+										 NRM_EQUAL,
 										 NUM_EXEC_QUAL((Plan *) join));
 	}
 	else if (IsA(join, HashJoin))
@@ -2273,6 +2320,7 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 										inner_itlist,
 										(Index) 0,
 										rtoffset,
+										NRM_EQUAL,
 										NUM_EXEC_QUAL((Plan *) join));
 
 		/*
@@ -2284,45 +2332,27 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 											   outer_itlist,
 											   OUTER_VAR,
 											   rtoffset,
+											   NRM_EQUAL,
 											   NUM_EXEC_QUAL((Plan *) join));
 	}
 
 	/*
 	 * Now we need to fix up the targetlist and qpqual, which are logically
-	 * above the join.  This means they should not re-use any input expression
-	 * that was computed in the nullable side of an outer join.  Vars and
-	 * PlaceHolderVars are fine, so we can implement this restriction just by
-	 * clearing has_non_vars in the indexed_tlist structs.
-	 *
-	 * XXX This is a grotty workaround for the fact that we don't clearly
-	 * distinguish between a Var appearing below an outer join and the "same"
-	 * Var appearing above it.  If we did, we'd not need to hack the matching
-	 * rules this way.
+	 * above the join.  This means that, if it's not an inner join, any Vars
+	 * and PHVs appearing here should have nullingrels that include the
+	 * effects of the outer join, ie they will have nullingrels equal to the
+	 * input Vars' nullingrels plus the bit added by the outer join.  We don't
+	 * currently have enough info available here to identify what that should
+	 * be, so we just tell fix_join_expr to accept superset nullingrels
+	 * matches instead of exact ones.
 	 */
-	switch (join->jointype)
-	{
-		case JOIN_LEFT:
-		case JOIN_SEMI:
-		case JOIN_ANTI:
-			inner_itlist->has_non_vars = false;
-			break;
-		case JOIN_RIGHT:
-			outer_itlist->has_non_vars = false;
-			break;
-		case JOIN_FULL:
-			outer_itlist->has_non_vars = false;
-			inner_itlist->has_non_vars = false;
-			break;
-		default:
-			break;
-	}
-
 	join->plan.targetlist = fix_join_expr(root,
 										  join->plan.targetlist,
 										  outer_itlist,
 										  inner_itlist,
 										  (Index) 0,
 										  rtoffset,
+										  (join->jointype == JOIN_INNER ? NRM_EQUAL : NRM_SUPERSET),
 										  NUM_EXEC_TLIST((Plan *) join));
 	join->plan.qual = fix_join_expr(root,
 									join->plan.qual,
@@ -2330,6 +2360,7 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
 									inner_itlist,
 									(Index) 0,
 									rtoffset,
+									(join->jointype == JOIN_INNER ? NRM_EQUAL : NRM_SUPERSET),
 									NUM_EXEC_QUAL((Plan *) join));
 
 	pfree(outer_itlist);
@@ -2384,6 +2415,7 @@ set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
 										 subplan_itlist,
 										 OUTER_VAR,
 										 rtoffset,
+										 NRM_EQUAL,
 										 NUM_EXEC_TLIST(plan));
 		}
 		else
@@ -2392,6 +2424,7 @@ set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
 									 subplan_itlist,
 									 OUTER_VAR,
 									 rtoffset,
+									 NRM_EQUAL,
 									 NUM_EXEC_TLIST(plan));
 		tle = flatCopyTargetEntry(tle);
 		tle->expr = (Expr *) newexpr;
@@ -2405,6 +2438,7 @@ set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
 					   subplan_itlist,
 					   OUTER_VAR,
 					   rtoffset,
+					   NRM_EQUAL,
 					   NUM_EXEC_QUAL(plan));
 
 	pfree(subplan_itlist);
@@ -2605,7 +2639,7 @@ set_dummy_tlist_references(Plan *plan, int rtoffset)
  * tlist_member() searches.
  *
  * The result of this function is an indexed_tlist struct to pass to
- * search_indexed_tlist_for_var() or search_indexed_tlist_for_non_var().
+ * search_indexed_tlist_for_var() and siblings.
  * When done, the indexed_tlist may be freed with a single pfree().
  */
 static indexed_tlist *
@@ -2637,6 +2671,9 @@ build_tlist_index(List *tlist)
 			vinfo->varno = var->varno;
 			vinfo->varattno = var->varattno;
 			vinfo->resno = tle->resno;
+#ifdef USE_ASSERT_CHECKING
+			vinfo->varnullingrels = var->varnullingrels;
+#endif
 			vinfo++;
 		}
 		else if (tle->expr && IsA(tle->expr, PlaceHolderVar))
@@ -2689,6 +2726,9 @@ build_tlist_index_other_vars(List *tlist, int ignore_rel)
 				vinfo->varno = var->varno;
 				vinfo->varattno = var->varattno;
 				vinfo->resno = tle->resno;
+#ifdef USE_ASSERT_CHECKING
+				vinfo->varnullingrels = var->varnullingrels;
+#endif
 				vinfo++;
 			}
 		}
@@ -2708,10 +2748,17 @@ build_tlist_index_other_vars(List *tlist, int ignore_rel)
  * modified varno/varattno (to wit, newvarno and the resno of the TLE entry).
  * Also ensure that varnosyn is incremented by rtoffset.
  * If no match, return NULL.
+ *
+ * In debugging builds, we cross-check the varnullingrels of the subplan
+ * output Var based on nrm_match.  Most call sites should pass NRM_EQUAL
+ * indicating we expect an exact match.  However, there are places where
+ * we haven't cleaned things up completely, and we have to settle for
+ * allowing subset or superset matches.
  */
 static Var *
 search_indexed_tlist_for_var(Var *var, indexed_tlist *itlist,
-							 int newvarno, int rtoffset)
+							 int newvarno, int rtoffset,
+							 NullingRelsMatch nrm_match)
 {
 	int			varno = var->varno;
 	AttrNumber	varattno = var->varattno;
@@ -2727,6 +2774,36 @@ search_indexed_tlist_for_var(Var *var, indexed_tlist *itlist,
 			/* Found a match */
 			Var		   *newvar = copyVar(var);
 
+			/*
+			 * Assert that we kept all the nullingrels machinations straight.
+			 *
+			 * XXX eventually reduce this to a plain Assert.  Right now it's
+			 * more useful to warn and keep going.
+			 *
+			 * XXX skip this check for system columns and whole-row Vars.
+			 * That's because such Vars might be row identity Vars, which are
+			 * generated without any varnullingrels.  It'd be hard to do
+			 * otherwise, since they're normally made very early in planning,
+			 * when we haven't looked at the jointree yet and don't know which
+			 * joins might null such Vars.  Doesn't seem worth the expense to
+			 * make them fully valid.  (While it's slightly annoying that we
+			 * thereby lose checking for user-written references to such
+			 * columns, it seems unlikely that a bug in nullingrels logic
+			 * would affect only system columns.)
+			 */
+#ifdef USE_ASSERT_CHECKING
+			if (!(varattno <= 0 ||
+				  (nrm_match == NRM_SUBSET ?
+				   bms_is_subset(var->varnullingrels, vinfo->varnullingrels) :
+				   nrm_match == NRM_SUPERSET ?
+				   bms_is_subset(vinfo->varnullingrels, var->varnullingrels) :
+				   bms_equal(vinfo->varnullingrels, var->varnullingrels))))
+				elog(WARNING, "bogus varnullingrels for (%d,%d): expected %s, found %s in subplan",
+					 varno, varattno,
+					 bmsToString(var->varnullingrels),
+					 bmsToString(vinfo->varnullingrels));
+#endif
+
 			newvar->varno = newvarno;
 			newvar->varattno = vinfo->resno;
 			if (newvar->varnosyn > 0)
@@ -2739,15 +2816,74 @@ search_indexed_tlist_for_var(Var *var, indexed_tlist *itlist,
 }
 
 /*
- * search_indexed_tlist_for_non_var --- find a non-Var in an indexed tlist
+ * search_indexed_tlist_for_phv --- find a PlaceHolderVar in an indexed tlist
  *
  * If a match is found, return a Var constructed to reference the tlist item.
  * If no match, return NULL.
  *
- * NOTE: it is a waste of time to call this unless itlist->has_ph_vars or
- * itlist->has_non_vars.  Furthermore, set_join_references() relies on being
- * able to prevent matching of non-Vars by clearing itlist->has_non_vars,
- * so there's a correctness reason not to call it unless that's set.
+ * Cross-check phnullingrels as in search_indexed_tlist_for_var.
+ *
+ * NOTE: it is a waste of time to call this unless itlist->has_ph_vars.
+ */
+static Var *
+search_indexed_tlist_for_phv(PlaceHolderVar *phv,
+							 indexed_tlist *itlist, int newvarno,
+							 NullingRelsMatch nrm_match)
+{
+	ListCell   *lc;
+
+	foreach(lc, itlist->tlist)
+	{
+		TargetEntry *tle = (TargetEntry *) lfirst(lc);
+
+		if (tle->expr && IsA(tle->expr, PlaceHolderVar))
+		{
+			PlaceHolderVar *subphv = (PlaceHolderVar *) tle->expr;
+			Var		   *newvar;
+
+			/*
+			 * Analogously to search_indexed_tlist_for_var, we match on phid
+			 * only.  We don't use equal(), partially for speed but mostly
+			 * because phnullingrels might not be exactly equal.
+			 */
+			if (phv->phid != subphv->phid)
+				continue;
+
+			/*
+			 * Assert that we kept all the nullingrels machinations straight.
+			 *
+			 * XXX eventually reduce this to a plain Assert.  Right now it's
+			 * more useful to warn and keep going.
+			 */
+#ifdef USE_ASSERT_CHECKING
+			if (!(nrm_match == NRM_SUBSET ?
+				  bms_is_subset(phv->phnullingrels, subphv->phnullingrels) :
+				  nrm_match == NRM_SUPERSET ?
+				  bms_is_subset(subphv->phnullingrels, phv->phnullingrels) :
+				  bms_equal(subphv->phnullingrels, phv->phnullingrels)))
+				elog(WARNING, "bogus phnullingrels for %d: expected %s, found %s in subplan",
+					 phv->phid,
+					 bmsToString(phv->phnullingrels),
+					 bmsToString(subphv->phnullingrels));
+#endif
+
+			/* Found a matching subplan output expression */
+			newvar = makeVarFromTargetEntry(newvarno, tle);
+			newvar->varnosyn = 0;	/* wasn't ever a plain Var */
+			newvar->varattnosyn = 0;
+			return newvar;
+		}
+	}
+	return NULL;				/* no match */
+}
+
+/*
+ * search_indexed_tlist_for_non_var --- find a non-Var/PHV in an indexed tlist
+ *
+ * If a match is found, return a Var constructed to reference the tlist item.
+ * If no match, return NULL.
+ *
+ * NOTE: it is a waste of time to call this unless itlist->has_non_vars.
  */
 static Var *
 search_indexed_tlist_for_non_var(Expr *node,
@@ -2854,6 +2990,7 @@ search_indexed_tlist_for_sortgroupref(Expr *node,
  * 'acceptable_rel' is either zero or the rangetable index of a relation
  *		whose Vars may appear in the clause without provoking an error
  * 'rtoffset': how much to increment varnos by
+ * 'nrm_match': as for search_indexed_tlist_for_var()
  * 'num_exec': estimated number of executions of expression
  *
  * Returns the new expression tree.  The original clause structure is
@@ -2866,6 +3003,7 @@ fix_join_expr(PlannerInfo *root,
 			  indexed_tlist *inner_itlist,
 			  Index acceptable_rel,
 			  int rtoffset,
+			  NullingRelsMatch nrm_match,
 			  double num_exec)
 {
 	fix_join_expr_context context;
@@ -2875,6 +3013,7 @@ fix_join_expr(PlannerInfo *root,
 	context.inner_itlist = inner_itlist;
 	context.acceptable_rel = acceptable_rel;
 	context.rtoffset = rtoffset;
+	context.nrm_match = nrm_match;
 	context.num_exec = num_exec;
 	return (List *) fix_join_expr_mutator((Node *) clauses, &context);
 }
@@ -2896,7 +3035,8 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
 			newvar = search_indexed_tlist_for_var(var,
 												  context->outer_itlist,
 												  OUTER_VAR,
-												  context->rtoffset);
+												  context->rtoffset,
+												  context->nrm_match);
 			if (newvar)
 				return (Node *) newvar;
 		}
@@ -2907,7 +3047,8 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
 			newvar = search_indexed_tlist_for_var(var,
 												  context->inner_itlist,
 												  INNER_VAR,
-												  context->rtoffset);
+												  context->rtoffset,
+												  context->nrm_match);
 			if (newvar)
 				return (Node *) newvar;
 		}
@@ -2932,22 +3073,25 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
 		/* See if the PlaceHolderVar has bubbled up from a lower plan node */
 		if (context->outer_itlist && context->outer_itlist->has_ph_vars)
 		{
-			newvar = search_indexed_tlist_for_non_var((Expr *) phv,
-													  context->outer_itlist,
-													  OUTER_VAR);
+			newvar = search_indexed_tlist_for_phv(phv,
+												  context->outer_itlist,
+												  OUTER_VAR,
+												  context->nrm_match);
 			if (newvar)
 				return (Node *) newvar;
 		}
 		if (context->inner_itlist && context->inner_itlist->has_ph_vars)
 		{
-			newvar = search_indexed_tlist_for_non_var((Expr *) phv,
-													  context->inner_itlist,
-													  INNER_VAR);
+			newvar = search_indexed_tlist_for_phv(phv,
+												  context->inner_itlist,
+												  INNER_VAR,
+												  context->nrm_match);
 			if (newvar)
 				return (Node *) newvar;
 		}
 
 		/* If not supplied by input plans, evaluate the contained expr */
+		/* XXX can we assert something about phnullingrels? */
 		return fix_join_expr_mutator((Node *) phv->phexpr, context);
 	}
 	/* Try matching more complex expressions too, if tlists have any */
@@ -3006,6 +3150,7 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
  * 'subplan_itlist': indexed target list for subplan (or index)
  * 'newvarno': varno to use for Vars referencing tlist elements
  * 'rtoffset': how much to increment varnos by
+ * 'nrm_match': as for search_indexed_tlist_for_var()
  * 'num_exec': estimated number of executions of expression
  *
  * The resulting tree is a copy of the original in which all Var nodes have
@@ -3018,6 +3163,7 @@ fix_upper_expr(PlannerInfo *root,
 			   indexed_tlist *subplan_itlist,
 			   int newvarno,
 			   int rtoffset,
+			   NullingRelsMatch nrm_match,
 			   double num_exec)
 {
 	fix_upper_expr_context context;
@@ -3026,6 +3172,7 @@ fix_upper_expr(PlannerInfo *root,
 	context.subplan_itlist = subplan_itlist;
 	context.newvarno = newvarno;
 	context.rtoffset = rtoffset;
+	context.nrm_match = nrm_match;
 	context.num_exec = num_exec;
 	return fix_upper_expr_mutator(node, &context);
 }
@@ -3044,7 +3191,8 @@ fix_upper_expr_mutator(Node *node, fix_upper_expr_context *context)
 		newvar = search_indexed_tlist_for_var(var,
 											  context->subplan_itlist,
 											  context->newvarno,
-											  context->rtoffset);
+											  context->rtoffset,
+											  context->nrm_match);
 		if (!newvar)
 			elog(ERROR, "variable not found in subplan target list");
 		return (Node *) newvar;
@@ -3056,13 +3204,15 @@ fix_upper_expr_mutator(Node *node, fix_upper_expr_context *context)
 		/* See if the PlaceHolderVar has bubbled up from a lower plan node */
 		if (context->subplan_itlist->has_ph_vars)
 		{
-			newvar = search_indexed_tlist_for_non_var((Expr *) phv,
-													  context->subplan_itlist,
-													  context->newvarno);
+			newvar = search_indexed_tlist_for_phv(phv,
+												  context->subplan_itlist,
+												  context->newvarno,
+												  context->nrm_match);
 			if (newvar)
 				return (Node *) newvar;
 		}
 		/* If not supplied by input plan, evaluate the contained expr */
+		/* XXX can we assert something about phnullingrels? */
 		return fix_upper_expr_mutator((Node *) phv->phexpr, context);
 	}
 	/* Try matching more complex expressions too, if tlist has any */
@@ -3169,6 +3319,7 @@ set_returning_clause_references(PlannerInfo *root,
 						  NULL,
 						  resultRelation,
 						  rtoffset,
+						  NRM_EQUAL,
 						  NUM_EXEC_TLIST(topplan));
 
 	pfree(itlist);
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 37a7af8c66..029172333e 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -51,17 +51,28 @@ typedef struct pullup_replace_vars_context
 								 * pullup (set only if target_rte->lateral) */
 	bool	   *outer_hasSubLinks;	/* -> outer query's hasSubLinks */
 	int			varno;			/* varno of subquery */
-	bool		need_phvs;		/* do we need PlaceHolderVars? */
-	bool		wrap_non_vars;	/* do we need 'em on *all* non-Vars? */
+	bool		wrap_non_vars;	/* do we need all non-Var outputs to be PHVs? */
 	Node	  **rv_cache;		/* cache for results with PHVs */
 } pullup_replace_vars_context;
 
-typedef struct reduce_outer_joins_state
+typedef struct reduce_outer_joins_pass1_state
 {
 	Relids		relids;			/* base relids within this subtree */
 	bool		contains_outer; /* does subtree contain outer join(s)? */
 	List	   *sub_states;		/* List of states for subtree components */
-} reduce_outer_joins_state;
+} reduce_outer_joins_pass1_state;
+
+typedef struct reduce_outer_joins_pass2_state
+{
+	Relids		inner_reduced;	/* OJ relids reduced to plain inner joins */
+	List	   *partial_reduced;	/* List of partially reduced FULL joins */
+} reduce_outer_joins_pass2_state;
+
+typedef struct reduce_outer_joins_partial_state
+{
+	int			full_join_rti;	/* RT index of a formerly-FULL join */
+	Relids		unreduced_side; /* relids in its still-nullable side */
+} reduce_outer_joins_partial_state;
 
 static Node *pull_up_sublinks_jointree_recurse(PlannerInfo *root, Node *jtnode,
 											   Relids *relids);
@@ -70,12 +81,10 @@ static Node *pull_up_sublinks_qual_recurse(PlannerInfo *root, Node *node,
 										   Node **jtlink2, Relids available_rels2);
 static Node *pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 										JoinExpr *lowest_outer_join,
-										JoinExpr *lowest_nulling_outer_join,
 										AppendRelInfo *containing_appendrel);
 static Node *pull_up_simple_subquery(PlannerInfo *root, Node *jtnode,
 									 RangeTblEntry *rte,
 									 JoinExpr *lowest_outer_join,
-									 JoinExpr *lowest_nulling_outer_join,
 									 AppendRelInfo *containing_appendrel);
 static Node *pull_up_simple_union_all(PlannerInfo *root, Node *jtnode,
 									  RangeTblEntry *rte);
@@ -92,7 +101,6 @@ static Node *pull_up_simple_values(PlannerInfo *root, Node *jtnode,
 static bool is_simple_values(PlannerInfo *root, RangeTblEntry *rte);
 static Node *pull_up_constant_function(PlannerInfo *root, Node *jtnode,
 									   RangeTblEntry *rte,
-									   JoinExpr *lowest_nulling_outer_join,
 									   AppendRelInfo *containing_appendrel);
 static bool is_simple_union_all(Query *subquery);
 static bool is_simple_union_all_recurse(Node *setOp, Query *setOpQuery,
@@ -103,24 +111,26 @@ static bool jointree_contains_lateral_outer_refs(PlannerInfo *root,
 												 Relids safe_upper_varnos);
 static void perform_pullup_replace_vars(PlannerInfo *root,
 										pullup_replace_vars_context *rvcontext,
-										JoinExpr *lowest_nulling_outer_join,
 										AppendRelInfo *containing_appendrel);
 static void replace_vars_in_jointree(Node *jtnode,
-									 pullup_replace_vars_context *context,
-									 JoinExpr *lowest_nulling_outer_join);
+									 pullup_replace_vars_context *context);
 static Node *pullup_replace_vars(Node *expr,
 								 pullup_replace_vars_context *context);
 static Node *pullup_replace_vars_callback(Var *var,
 										  replace_rte_variables_context *context);
 static Query *pullup_replace_vars_subquery(Query *query,
 										   pullup_replace_vars_context *context);
-static reduce_outer_joins_state *reduce_outer_joins_pass1(Node *jtnode);
+static reduce_outer_joins_pass1_state *reduce_outer_joins_pass1(Node *jtnode);
 static void reduce_outer_joins_pass2(Node *jtnode,
-									 reduce_outer_joins_state *state,
+									 reduce_outer_joins_pass1_state *state1,
+									 reduce_outer_joins_pass2_state *state2,
 									 PlannerInfo *root,
 									 Relids nonnullable_rels,
 									 List *forced_null_vars);
-static Node *remove_useless_results_recurse(PlannerInfo *root, Node *jtnode);
+static void report_reduced_full_join(reduce_outer_joins_pass2_state *state2,
+									 int rtindex, Relids relids);
+static Node *remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
+											Relids *dropped_outer_joins);
 static int	get_result_relid(PlannerInfo *root, Node *jtnode);
 static void remove_result_refs(PlannerInfo *root, int varno, Node *newjtloc);
 static bool find_dependent_phvs(PlannerInfo *root, int varno);
@@ -761,7 +771,7 @@ pull_up_subqueries(PlannerInfo *root)
 	/* Recursion starts with no containing join nor appendrel */
 	root->parse->jointree = (FromExpr *)
 		pull_up_subqueries_recurse(root, (Node *) root->parse->jointree,
-								   NULL, NULL, NULL);
+								   NULL, NULL);
 	/* We should still have a FromExpr */
 	Assert(IsA(root->parse->jointree, FromExpr));
 }
@@ -776,12 +786,6 @@ pull_up_subqueries(PlannerInfo *root)
  * lowest_outer_join references the lowest such JoinExpr node; otherwise
  * it is NULL.  We use this to constrain the effects of LATERAL subqueries.
  *
- * If this jointree node is within the nullable side of an outer join, then
- * lowest_nulling_outer_join references the lowest such JoinExpr node;
- * otherwise it is NULL.  This forces use of the PlaceHolderVar mechanism for
- * references to non-nullable targetlist items, but only for references above
- * that join.
- *
  * If we are looking at a member subquery of an append relation,
  * containing_appendrel describes that relation; else it is NULL.
  * This forces use of the PlaceHolderVar mechanism for all non-Var targetlist
@@ -798,15 +802,14 @@ pull_up_subqueries(PlannerInfo *root)
  * Notice also that we can't turn pullup_replace_vars loose on the whole
  * jointree, because it'd return a mutated copy of the tree; we have to
  * invoke it just on the quals, instead.  This behavior is what makes it
- * reasonable to pass lowest_outer_join and lowest_nulling_outer_join as
- * pointers rather than some more-indirect way of identifying the lowest
- * OJs.  Likewise, we don't replace append_rel_list members but only their
- * substructure, so the containing_appendrel reference is safe to use.
+ * reasonable to pass lowest_outer_join as a pointer rather than some
+ * more-indirect way of identifying the lowest OJ.  Likewise, we don't
+ * replace append_rel_list members but only their substructure, so the
+ * containing_appendrel reference is safe to use.
  */
 static Node *
 pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 						   JoinExpr *lowest_outer_join,
-						   JoinExpr *lowest_nulling_outer_join,
 						   AppendRelInfo *containing_appendrel)
 {
 	/* Since this function recurses, it could be driven to stack overflow. */
@@ -833,7 +836,6 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 			 is_safe_append_member(rte->subquery)))
 			return pull_up_simple_subquery(root, jtnode, rte,
 										   lowest_outer_join,
-										   lowest_nulling_outer_join,
 										   containing_appendrel);
 
 		/*
@@ -866,7 +868,6 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 		 */
 		if (rte->rtekind == RTE_FUNCTION)
 			return pull_up_constant_function(root, jtnode, rte,
-											 lowest_nulling_outer_join,
 											 containing_appendrel);
 
 		/* Otherwise, do nothing at this node. */
@@ -882,7 +883,6 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 		{
 			lfirst(l) = pull_up_subqueries_recurse(root, lfirst(l),
 												   lowest_outer_join,
-												   lowest_nulling_outer_join,
 												   NULL);
 		}
 	}
@@ -897,11 +897,9 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 			case JOIN_INNER:
 				j->larg = pull_up_subqueries_recurse(root, j->larg,
 													 lowest_outer_join,
-													 lowest_nulling_outer_join,
 													 NULL);
 				j->rarg = pull_up_subqueries_recurse(root, j->rarg,
 													 lowest_outer_join,
-													 lowest_nulling_outer_join,
 													 NULL);
 				break;
 			case JOIN_LEFT:
@@ -909,31 +907,25 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 			case JOIN_ANTI:
 				j->larg = pull_up_subqueries_recurse(root, j->larg,
 													 j,
-													 lowest_nulling_outer_join,
 													 NULL);
 				j->rarg = pull_up_subqueries_recurse(root, j->rarg,
-													 j,
 													 j,
 													 NULL);
 				break;
 			case JOIN_FULL:
 				j->larg = pull_up_subqueries_recurse(root, j->larg,
-													 j,
 													 j,
 													 NULL);
 				j->rarg = pull_up_subqueries_recurse(root, j->rarg,
-													 j,
 													 j,
 													 NULL);
 				break;
 			case JOIN_RIGHT:
 				j->larg = pull_up_subqueries_recurse(root, j->larg,
-													 j,
 													 j,
 													 NULL);
 				j->rarg = pull_up_subqueries_recurse(root, j->rarg,
 													 j,
-													 lowest_nulling_outer_join,
 													 NULL);
 				break;
 			default:
@@ -963,7 +955,6 @@ pull_up_subqueries_recurse(PlannerInfo *root, Node *jtnode,
 static Node *
 pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 						JoinExpr *lowest_outer_join,
-						JoinExpr *lowest_nulling_outer_join,
 						AppendRelInfo *containing_appendrel)
 {
 	Query	   *parse = root->parse;
@@ -1112,31 +1103,25 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	 * The subquery's targetlist items are now in the appropriate form to
 	 * insert into the top query, except that we may need to wrap them in
 	 * PlaceHolderVars.  Set up required context data for pullup_replace_vars.
+	 * (Note that we should include the subquery's inner joins in relids,
+	 * since it may include join alias vars referencing them.)
 	 */
 	rvcontext.root = root;
 	rvcontext.targetlist = subquery->targetList;
 	rvcontext.target_rte = rte;
 	if (rte->lateral)
 		rvcontext.relids = get_relids_in_jointree((Node *) subquery->jointree,
-												  true);
+												  true, true);
 	else						/* won't need relids */
 		rvcontext.relids = NULL;
 	rvcontext.outer_hasSubLinks = &parse->hasSubLinks;
 	rvcontext.varno = varno;
-	/* these flags will be set below, if needed */
-	rvcontext.need_phvs = false;
+	/* this flag will be set below, if needed */
 	rvcontext.wrap_non_vars = false;
 	/* initialize cache array with indexes 0 .. length(tlist) */
 	rvcontext.rv_cache = palloc0((list_length(subquery->targetList) + 1) *
 								 sizeof(Node *));
 
-	/*
-	 * If we are under an outer join then non-nullable items and lateral
-	 * references may have to be turned into PlaceHolderVars.
-	 */
-	if (lowest_nulling_outer_join != NULL)
-		rvcontext.need_phvs = true;
-
 	/*
 	 * If we are dealing with an appendrel member then anything that's not a
 	 * simple Var has to be turned into a PlaceHolderVar.  We force this to
@@ -1145,10 +1130,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	 * expression actually available from the appendrel.
 	 */
 	if (containing_appendrel != NULL)
-	{
-		rvcontext.need_phvs = true;
 		rvcontext.wrap_non_vars = true;
-	}
 
 	/*
 	 * If the parent query uses grouping sets, we need a PlaceHolderVar for
@@ -1160,10 +1142,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	 * that pullup_replace_vars hasn't currently got.)
 	 */
 	if (parse->groupingSets)
-	{
-		rvcontext.need_phvs = true;
 		rvcontext.wrap_non_vars = true;
-	}
 
 	/*
 	 * Replace all of the top query's references to the subquery's outputs
@@ -1171,7 +1150,6 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	 * replace any of the jointree structure.
 	 */
 	perform_pullup_replace_vars(root, &rvcontext,
-								lowest_nulling_outer_join,
 								containing_appendrel);
 
 	/*
@@ -1238,7 +1216,8 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	{
 		Relids		subrelids;
 
-		subrelids = get_relids_in_jointree((Node *) subquery->jointree, false);
+		subrelids = get_relids_in_jointree((Node *) subquery->jointree,
+										   true, false);
 		if (root->glob->lastPHId != 0)
 			substitute_phv_relids((Node *) parse, varno, subrelids);
 		fix_append_rel_relids(root, varno, subrelids);
@@ -1434,7 +1413,7 @@ pull_up_union_leaf_queries(Node *setOp, PlannerInfo *root, int parentRTindex,
 		rtr = makeNode(RangeTblRef);
 		rtr->rtindex = childRTindex;
 		(void) pull_up_subqueries_recurse(root, (Node *) rtr,
-										  NULL, NULL, appinfo);
+										  NULL, appinfo);
 	}
 	else if (IsA(setOp, SetOperationStmt))
 	{
@@ -1571,7 +1550,7 @@ is_simple_subquery(PlannerInfo *root, Query *subquery, RangeTblEntry *rte,
 		{
 			restricted = true;
 			safe_upper_varnos = get_relids_in_jointree((Node *) lowest_outer_join,
-													   true);
+													   true, true);
 		}
 		else
 		{
@@ -1683,7 +1662,6 @@ pull_up_simple_values(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte)
 	rvcontext.relids = NULL;
 	rvcontext.outer_hasSubLinks = &parse->hasSubLinks;
 	rvcontext.varno = varno;
-	rvcontext.need_phvs = false;
 	rvcontext.wrap_non_vars = false;
 	/* initialize cache array with indexes 0 .. length(tlist) */
 	rvcontext.rv_cache = palloc0((list_length(tlist) + 1) *
@@ -1695,7 +1673,7 @@ pull_up_simple_values(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte)
 	 * any of the jointree structure.  We can assume there's no outer joins or
 	 * appendrels in the dummy Query that surrounds a VALUES RTE.
 	 */
-	perform_pullup_replace_vars(root, &rvcontext, NULL, NULL);
+	perform_pullup_replace_vars(root, &rvcontext, NULL);
 
 	/*
 	 * There should be no appendrels to fix, nor any outer joins and hence no
@@ -1794,7 +1772,6 @@ is_simple_values(PlannerInfo *root, RangeTblEntry *rte)
 static Node *
 pull_up_constant_function(PlannerInfo *root, Node *jtnode,
 						  RangeTblEntry *rte,
-						  JoinExpr *lowest_nulling_outer_join,
 						  AppendRelInfo *containing_appendrel)
 {
 	Query	   *parse = root->parse;
@@ -1846,40 +1823,26 @@ pull_up_constant_function(PlannerInfo *root, Node *jtnode,
 
 	rvcontext.outer_hasSubLinks = &parse->hasSubLinks;
 	rvcontext.varno = ((RangeTblRef *) jtnode)->rtindex;
-	/* these flags will be set below, if needed */
-	rvcontext.need_phvs = false;
+	/* this flag will be set below, if needed */
 	rvcontext.wrap_non_vars = false;
 	/* initialize cache array with indexes 0 .. length(tlist) */
 	rvcontext.rv_cache = palloc0((list_length(rvcontext.targetlist) + 1) *
 								 sizeof(Node *));
 
-	/*
-	 * If we are under an outer join then non-nullable items and lateral
-	 * references may have to be turned into PlaceHolderVars.
-	 */
-	if (lowest_nulling_outer_join != NULL)
-		rvcontext.need_phvs = true;
-
 	/*
 	 * If we are dealing with an appendrel member then anything that's not a
 	 * simple Var has to be turned into a PlaceHolderVar.  (See comments in
 	 * pull_up_simple_subquery().)
 	 */
 	if (containing_appendrel != NULL)
-	{
-		rvcontext.need_phvs = true;
 		rvcontext.wrap_non_vars = true;
-	}
 
 	/*
 	 * If the parent query uses grouping sets, we need a PlaceHolderVar for
 	 * anything that's not a simple Var.
 	 */
 	if (parse->groupingSets)
-	{
-		rvcontext.need_phvs = true;
 		rvcontext.wrap_non_vars = true;
-	}
 
 	/*
 	 * Replace all of the top query's references to the RTE's output with
@@ -1887,7 +1850,6 @@ pull_up_constant_function(PlannerInfo *root, Node *jtnode,
 	 * jointree structure.
 	 */
 	perform_pullup_replace_vars(root, &rvcontext,
-								lowest_nulling_outer_join,
 								containing_appendrel);
 
 	/*
@@ -2112,13 +2074,11 @@ jointree_contains_lateral_outer_refs(PlannerInfo *root, Node *jtnode,
  *
  * Caller has already filled *rvcontext with data describing what to
  * substitute for Vars referencing the target subquery.  In addition
- * we need the identity of the lowest outer join that can null the
- * target subquery, and its containing appendrel if any.
+ * we need the identity of the containing appendrel if any.
  */
 static void
 perform_pullup_replace_vars(PlannerInfo *root,
 							pullup_replace_vars_context *rvcontext,
-							JoinExpr *lowest_nulling_outer_join,
 							AppendRelInfo *containing_appendrel)
 {
 	Query	   *parse = root->parse;
@@ -2128,18 +2088,18 @@ perform_pullup_replace_vars(PlannerInfo *root,
 	 * If we are considering an appendrel child subquery (that is, a UNION ALL
 	 * member query that we're pulling up), then the only part of the upper
 	 * query that could reference the child yet is the translated_vars list of
-	 * the associated AppendRelInfo.  Furthermore, we do not need to insert
-	 * PHVs in the AppendRelInfo --- there isn't any outer join between.
+	 * the associated AppendRelInfo.  Furthermore, we do not want to force use
+	 * of PHVs in the AppendRelInfo --- there isn't any outer join between.
 	 */
 	if (containing_appendrel)
 	{
-		bool		save_need_phvs = rvcontext->need_phvs;
+		bool		save_wrap_non_vars = rvcontext->wrap_non_vars;
 
-		rvcontext->need_phvs = false;
+		rvcontext->wrap_non_vars = false;
 		containing_appendrel->translated_vars = (List *)
 			pullup_replace_vars((Node *) containing_appendrel->translated_vars,
 								rvcontext);
-		rvcontext->need_phvs = save_need_phvs;
+		rvcontext->wrap_non_vars = save_wrap_non_vars;
 		return;
 	}
 
@@ -2190,8 +2150,7 @@ perform_pullup_replace_vars(PlannerInfo *root,
 				pullup_replace_vars((Node *) action->targetList, rvcontext);
 		}
 	}
-	replace_vars_in_jointree((Node *) parse->jointree, rvcontext,
-							 lowest_nulling_outer_join);
+	replace_vars_in_jointree((Node *) parse->jointree, rvcontext);
 	Assert(parse->setOperations == NULL);
 	parse->havingQual = pullup_replace_vars(parse->havingQual, rvcontext);
 
@@ -2208,12 +2167,6 @@ perform_pullup_replace_vars(PlannerInfo *root,
 
 	/*
 	 * Replace references in the joinaliasvars lists of join RTEs.
-	 *
-	 * You might think that we could avoid using PHVs for alias vars of joins
-	 * below lowest_nulling_outer_join, but that doesn't work because the
-	 * alias vars could be referenced above that join; we need the PHVs to be
-	 * present in such references after the alias vars get flattened.  (It
-	 * might be worth trying to be smarter here, someday.)
 	 */
 	foreach(lc, parse->rtable)
 	{
@@ -2230,14 +2183,10 @@ perform_pullup_replace_vars(PlannerInfo *root,
  * Helper routine for perform_pullup_replace_vars: do pullup_replace_vars on
  * every expression in the jointree, without changing the jointree structure
  * itself.  Ugly, but there's no other way...
- *
- * If we are at or below lowest_nulling_outer_join, we can suppress use of
- * PlaceHolderVars wrapped around the replacement expressions.
  */
 static void
 replace_vars_in_jointree(Node *jtnode,
-						 pullup_replace_vars_context *context,
-						 JoinExpr *lowest_nulling_outer_join)
+						 pullup_replace_vars_context *context)
 {
 	if (jtnode == NULL)
 		return;
@@ -2247,10 +2196,8 @@ replace_vars_in_jointree(Node *jtnode,
 		 * If the RangeTblRef refers to a LATERAL subquery (that isn't the
 		 * same subquery we're pulling up), it might contain references to the
 		 * target subquery, which we must replace.  We drive this from the
-		 * jointree scan, rather than a scan of the rtable, for a couple of
-		 * reasons: we can avoid processing no-longer-referenced RTEs, and we
-		 * can use the appropriate setting of need_phvs depending on whether
-		 * the RTE is above possibly-nulling outer joins or not.
+		 * jointree scan, rather than a scan of the rtable, so that we can
+		 * avoid processing no-longer-referenced RTEs.
 		 */
 		int			varno = ((RangeTblRef *) jtnode)->rtindex;
 
@@ -2307,42 +2254,30 @@ replace_vars_in_jointree(Node *jtnode,
 		ListCell   *l;
 
 		foreach(l, f->fromlist)
-			replace_vars_in_jointree(lfirst(l), context,
-									 lowest_nulling_outer_join);
+			replace_vars_in_jointree(lfirst(l), context);
 		f->quals = pullup_replace_vars(f->quals, context);
 	}
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
-		bool		save_need_phvs = context->need_phvs;
+		bool		save_wrap_non_vars = context->wrap_non_vars;
 
-		if (j == lowest_nulling_outer_join)
-		{
-			/* no more PHVs in or below this join */
-			context->need_phvs = false;
-			lowest_nulling_outer_join = NULL;
-		}
-		replace_vars_in_jointree(j->larg, context, lowest_nulling_outer_join);
-		replace_vars_in_jointree(j->rarg, context, lowest_nulling_outer_join);
+		replace_vars_in_jointree(j->larg, context);
+		replace_vars_in_jointree(j->rarg, context);
 
 		/*
-		 * Use PHVs within the join quals of a full join, even when it's the
-		 * lowest nulling outer join.  Otherwise, we cannot identify which
-		 * side of the join a pulled-up var-free expression came from, which
-		 * can lead to failure to make a plan at all because none of the quals
-		 * appear to be mergeable or hashable conditions.  For this purpose we
-		 * don't care about the state of wrap_non_vars, so leave it alone.
+		 * Use PHVs within the join quals of a full join.  Otherwise, we
+		 * cannot identify which side of the join a pulled-up var-free
+		 * expression came from, which can lead to failure to make a plan at
+		 * all because none of the quals appear to be mergeable or hashable
+		 * conditions.
 		 */
 		if (j->jointype == JOIN_FULL)
-			context->need_phvs = true;
+			context->wrap_non_vars = true;
 
 		j->quals = pullup_replace_vars(j->quals, context);
 
-		/*
-		 * We don't bother to update the colvars list, since it won't be used
-		 * again ...
-		 */
-		context->need_phvs = save_need_phvs;
+		context->wrap_non_vars = save_wrap_non_vars;
 	}
 	else
 		elog(ERROR, "unrecognized node type: %d",
@@ -2371,8 +2306,18 @@ pullup_replace_vars_callback(Var *var,
 {
 	pullup_replace_vars_context *rcon = (pullup_replace_vars_context *) context->callback_arg;
 	int			varattno = var->varattno;
+	bool		need_phv;
 	Node	   *newnode;
 
+	/*
+	 * We need a PlaceHolderVar if the Var-to-be-replaced has nonempty
+	 * varnullingrels (unless we find below that the replacement expression is
+	 * a Var or PlaceHolderVar that we can just add the nullingrels to).  We
+	 * also need one if the caller has instructed us that all non-Var/PHV
+	 * replacements need to be wrapped for identification purposes.
+	 */
+	need_phv = (var->varnullingrels != NULL) || rcon->wrap_non_vars;
+
 	/*
 	 * If PlaceHolderVars are needed, we cache the modified expressions in
 	 * rcon->rv_cache[].  This is not in hopes of any material speed gain
@@ -2381,13 +2326,16 @@ pullup_replace_vars_callback(Var *var,
 	 * and possibly prevent optimizations that rely on recognizing different
 	 * references to the same subquery output as being equal().  So it's worth
 	 * a bit of extra effort to avoid it.
+	 *
+	 * The cached items have phlevelsup = 0 and phnullingrels = NULL; we'll
+	 * copy them and adjust those values for this reference site below.
 	 */
-	if (rcon->need_phvs &&
+	if (need_phv &&
 		varattno >= InvalidAttrNumber &&
 		varattno <= list_length(rcon->targetlist) &&
 		rcon->rv_cache[varattno] != NULL)
 	{
-		/* Just copy the entry and fall through to adjust its varlevelsup */
+		/* Just copy the entry and fall through to adjust phlevelsup etc */
 		newnode = copyObject(rcon->rv_cache[varattno]);
 	}
 	else if (varattno == InvalidAttrNumber)
@@ -2396,7 +2344,7 @@ pullup_replace_vars_callback(Var *var,
 		RowExpr    *rowexpr;
 		List	   *colnames;
 		List	   *fields;
-		bool		save_need_phvs = rcon->need_phvs;
+		bool		save_wrap_non_vars = rcon->wrap_non_vars;
 		int			save_sublevelsup = context->sublevels_up;
 
 		/*
@@ -2407,18 +2355,18 @@ pullup_replace_vars_callback(Var *var,
 		 * the RowExpr for use of the executor and ruleutils.c.
 		 *
 		 * In order to be able to cache the results, we always generate the
-		 * expansion with varlevelsup = 0, and then adjust if needed.
+		 * expansion with varlevelsup = 0, and then adjust below if needed.
 		 */
 		expandRTE(rcon->target_rte,
 				  var->varno, 0 /* not varlevelsup */ , var->location,
 				  (var->vartype != RECORDOID),
 				  &colnames, &fields);
-		/* Adjust the generated per-field Vars, but don't insert PHVs */
-		rcon->need_phvs = false;
+		/* Expand the generated per-field Vars, but don't insert PHVs there */
+		rcon->wrap_non_vars = false;
 		context->sublevels_up = 0;	/* to match the expandRTE output */
 		fields = (List *) replace_rte_variables_mutator((Node *) fields,
 														context);
-		rcon->need_phvs = save_need_phvs;
+		rcon->wrap_non_vars = save_wrap_non_vars;
 		context->sublevels_up = save_sublevelsup;
 
 		rowexpr = makeNode(RowExpr);
@@ -2436,14 +2384,13 @@ pullup_replace_vars_callback(Var *var,
 		 * expression to yield NULL, not ROW(NULL,NULL,...) when it is forced
 		 * to null by an outer join.
 		 */
-		if (rcon->need_phvs)
+		if (need_phv)
 		{
-			/* RowExpr is certainly not strict, so always need PHV */
 			newnode = (Node *)
 				make_placeholder_expr(rcon->root,
 									  (Expr *) newnode,
 									  bms_make_singleton(rcon->varno));
-			/* cache it with the PHV, and with varlevelsup still zero */
+			/* cache it with the PHV, and with phlevelsup etc not set yet */
 			rcon->rv_cache[InvalidAttrNumber] = copyObject(newnode);
 		}
 	}
@@ -2460,7 +2407,7 @@ pullup_replace_vars_callback(Var *var,
 		newnode = (Node *) copyObject(tle->expr);
 
 		/* Insert PlaceHolderVar if needed */
-		if (rcon->need_phvs)
+		if (need_phv)
 		{
 			bool		wrap;
 
@@ -2486,69 +2433,61 @@ pullup_replace_vars_callback(Var *var,
 				/* No need to wrap a PlaceHolderVar with another one, either */
 				wrap = false;
 			}
-			else if (rcon->wrap_non_vars)
-			{
-				/* Wrap all non-Vars in a PlaceHolderVar */
-				wrap = true;
-			}
 			else
 			{
 				/*
-				 * If it contains a Var of the subquery being pulled up, and
-				 * does not contain any non-strict constructs, then it's
-				 * certainly nullable so we don't need to insert a
-				 * PlaceHolderVar.
-				 *
-				 * This analysis could be tighter: in particular, a non-strict
-				 * construct hidden within a lower-level PlaceHolderVar is not
-				 * reason to add another PHV.  But for now it doesn't seem
-				 * worth the code to be more exact.
-				 *
-				 * Note: in future maybe we should insert a PlaceHolderVar
-				 * anyway, if the tlist item is expensive to evaluate?
-				 *
-				 * For a LATERAL subquery, we have to check the actual var
-				 * membership of the node, but if it's non-lateral then any
-				 * level-zero var must belong to the subquery.
+				 * Must wrap, either because we need a place to insert
+				 * varnullingrels or because caller told us to wrap
+				 * everything.
 				 */
-				if ((rcon->target_rte->lateral ?
-					 bms_overlap(pull_varnos(rcon->root, (Node *) newnode),
-								 rcon->relids) :
-					 contain_vars_of_level((Node *) newnode, 0)) &&
-					!contain_nonstrict_functions((Node *) newnode))
-				{
-					/* No wrap needed */
-					wrap = false;
-				}
-				else
-				{
-					/* Else wrap it in a PlaceHolderVar */
-					wrap = true;
-				}
+				wrap = true;
 			}
 
 			if (wrap)
+			{
 				newnode = (Node *)
 					make_placeholder_expr(rcon->root,
 										  (Expr *) newnode,
 										  bms_make_singleton(rcon->varno));
 
-			/*
-			 * Cache it if possible (ie, if the attno is in range, which it
-			 * probably always should be).  We can cache the value even if we
-			 * decided we didn't need a PHV, since this result will be
-			 * suitable for any request that has need_phvs.
-			 */
-			if (varattno > InvalidAttrNumber &&
-				varattno <= list_length(rcon->targetlist))
-				rcon->rv_cache[varattno] = copyObject(newnode);
+				/*
+				 * Cache it if possible (ie, if the attno is in range, which
+				 * it probably always should be).
+				 */
+				if (varattno > InvalidAttrNumber &&
+					varattno <= list_length(rcon->targetlist))
+					rcon->rv_cache[varattno] = copyObject(newnode);
+			}
 		}
 	}
 
-	/* Must adjust varlevelsup if tlist item is from higher query */
+	/* Must adjust varlevelsup if replaced Var is within a subquery */
 	if (var->varlevelsup > 0)
 		IncrementVarSublevelsUp(newnode, var->varlevelsup, 0);
 
+	/* Propagate any varnullingrels into the replacement Var or PHV */
+	if (var->varnullingrels != NULL)
+	{
+		if (IsA(newnode, Var))
+		{
+			Var		   *newvar = (Var *) newnode;
+
+			Assert(newvar->varlevelsup == var->varlevelsup);
+			newvar->varnullingrels = bms_add_members(newvar->varnullingrels,
+													 var->varnullingrels);
+		}
+		else if (IsA(newnode, PlaceHolderVar))
+		{
+			PlaceHolderVar *newphv = (PlaceHolderVar *) newnode;
+
+			Assert(newphv->phlevelsup == var->varlevelsup);
+			newphv->phnullingrels = bms_add_members(newphv->phnullingrels,
+													var->varnullingrels);
+		}
+		else
+			elog(ERROR, "failed to wrap a non-Var");
+	}
+
 	return newnode;
 }
 
@@ -2707,7 +2646,9 @@ flatten_simple_union_all(PlannerInfo *root)
 void
 reduce_outer_joins(PlannerInfo *root)
 {
-	reduce_outer_joins_state *state;
+	reduce_outer_joins_pass1_state *state1;
+	reduce_outer_joins_pass2_state state2;
+	ListCell   *lc;
 
 	/*
 	 * To avoid doing strictness checks on more quals than necessary, we want
@@ -2718,14 +2659,56 @@ reduce_outer_joins(PlannerInfo *root)
 	 * join(s) below each side of each join clause. The second pass examines
 	 * qual clauses and changes join types as it descends the tree.
 	 */
-	state = reduce_outer_joins_pass1((Node *) root->parse->jointree);
+	state1 = reduce_outer_joins_pass1((Node *) root->parse->jointree);
 
 	/* planner.c shouldn't have called me if no outer joins */
-	if (state == NULL || !state->contains_outer)
+	if (state1 == NULL || !state1->contains_outer)
 		elog(ERROR, "so where are the outer joins?");
 
+	state2.inner_reduced = NULL;
+	state2.partial_reduced = NIL;
+
 	reduce_outer_joins_pass2((Node *) root->parse->jointree,
-							 state, root, NULL, NIL);
+							 state1, &state2,
+							 root, NULL, NIL);
+
+	/*
+	 * If we successfully reduced the strength of any outer joins, we must
+	 * remove references to those joins as nulling rels.  This is handled as
+	 * an additional pass, for simplicity and because we can handle all
+	 * fully-reduced joins in a single pass over the parse tree.
+	 */
+	if (!bms_is_empty(state2.inner_reduced))
+	{
+		root->parse = (Query *)
+			remove_nulling_relids((Node *) root->parse,
+								  state2.inner_reduced,
+								  NULL);
+		/* There could be references in the append_rel_list, too */
+		root->append_rel_list = (List *)
+			remove_nulling_relids((Node *) root->append_rel_list,
+								  state2.inner_reduced,
+								  NULL);
+	}
+
+	/*
+	 * Partially-reduced full joins have to be done one at a time, since
+	 * they'll each need a different setting of except_relids.
+	 */
+	foreach(lc, state2.partial_reduced)
+	{
+		reduce_outer_joins_partial_state *statep = lfirst(lc);
+		Relids		full_join_relids = bms_make_singleton(statep->full_join_rti);
+
+		root->parse = (Query *)
+			remove_nulling_relids((Node *) root->parse,
+								  full_join_relids,
+								  statep->unreduced_side);
+		root->append_rel_list = (List *)
+			remove_nulling_relids((Node *) root->append_rel_list,
+								  full_join_relids,
+								  statep->unreduced_side);
+	}
 }
 
 /*
@@ -2733,13 +2716,13 @@ reduce_outer_joins(PlannerInfo *root)
  *
  * Returns a state node describing the given jointree node.
  */
-static reduce_outer_joins_state *
+static reduce_outer_joins_pass1_state *
 reduce_outer_joins_pass1(Node *jtnode)
 {
-	reduce_outer_joins_state *result;
+	reduce_outer_joins_pass1_state *result;
 
-	result = (reduce_outer_joins_state *)
-		palloc(sizeof(reduce_outer_joins_state));
+	result = (reduce_outer_joins_pass1_state *)
+		palloc(sizeof(reduce_outer_joins_pass1_state));
 	result->relids = NULL;
 	result->contains_outer = false;
 	result->sub_states = NIL;
@@ -2759,7 +2742,7 @@ reduce_outer_joins_pass1(Node *jtnode)
 
 		foreach(l, f->fromlist)
 		{
-			reduce_outer_joins_state *sub_state;
+			reduce_outer_joins_pass1_state *sub_state;
 
 			sub_state = reduce_outer_joins_pass1(lfirst(l));
 			result->relids = bms_add_members(result->relids,
@@ -2771,7 +2754,7 @@ reduce_outer_joins_pass1(Node *jtnode)
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
-		reduce_outer_joins_state *sub_state;
+		reduce_outer_joins_pass1_state *sub_state;
 
 		/* join's own RT index is not wanted in result->relids */
 		if (IS_OUTER_JOIN(j->jointype))
@@ -2799,14 +2782,22 @@ reduce_outer_joins_pass1(Node *jtnode)
  * reduce_outer_joins_pass2 - phase 2 processing
  *
  *	jtnode: current jointree node
- *	state: state data collected by phase 1 for this node
+ *	state1: state data collected by phase 1 for this node
+ *	state2: where to accumulate info about successfully-reduced joins
  *	root: toplevel planner state
  *	nonnullable_rels: set of base relids forced non-null by upper quals
  *	forced_null_vars: multibitmapset of Vars forced null by upper quals
+ *
+ * Returns info in state2 about outer joins that were successfully simplified.
+ * Joins that were fully reduced to inner joins are all added to
+ * state2->inner_reduced.  If a full join is reduced to a left join,
+ * it needs its own entry in state2->partial_reduced, since that will
+ * require custom processing to remove only the correct nullingrel markers.
  */
 static void
 reduce_outer_joins_pass2(Node *jtnode,
-						 reduce_outer_joins_state *state,
+						 reduce_outer_joins_pass1_state *state1,
+						 reduce_outer_joins_pass2_state *state2,
 						 PlannerInfo *root,
 						 Relids nonnullable_rels,
 						 List *forced_null_vars)
@@ -2835,13 +2826,14 @@ reduce_outer_joins_pass2(Node *jtnode,
 		pass_forced_null_vars = mbms_add_members(pass_forced_null_vars,
 												 forced_null_vars);
 		/* And recurse --- but only into interesting subtrees */
-		Assert(list_length(f->fromlist) == list_length(state->sub_states));
-		forboth(l, f->fromlist, s, state->sub_states)
+		Assert(list_length(f->fromlist) == list_length(state1->sub_states));
+		forboth(l, f->fromlist, s, state1->sub_states)
 		{
-			reduce_outer_joins_state *sub_state = lfirst(s);
+			reduce_outer_joins_pass1_state *sub_state = lfirst(s);
 
 			if (sub_state->contains_outer)
-				reduce_outer_joins_pass2(lfirst(l), sub_state, root,
+				reduce_outer_joins_pass2(lfirst(l), sub_state,
+										 state2, root,
 										 pass_nonnullable_rels,
 										 pass_forced_null_vars);
 		}
@@ -2853,8 +2845,8 @@ reduce_outer_joins_pass2(Node *jtnode,
 		JoinExpr   *j = (JoinExpr *) jtnode;
 		int			rtindex = j->rtindex;
 		JoinType	jointype = j->jointype;
-		reduce_outer_joins_state *left_state = linitial(state->sub_states);
-		reduce_outer_joins_state *right_state = lsecond(state->sub_states);
+		reduce_outer_joins_pass1_state *left_state = linitial(state1->sub_states);
+		reduce_outer_joins_pass1_state *right_state = lsecond(state1->sub_states);
 
 		/* Can we simplify this join? */
 		switch (jointype)
@@ -2875,12 +2867,22 @@ reduce_outer_joins_pass2(Node *jtnode,
 					if (bms_overlap(nonnullable_rels, right_state->relids))
 						jointype = JOIN_INNER;
 					else
+					{
 						jointype = JOIN_LEFT;
+						/* Also report partial reduction in state2 */
+						report_reduced_full_join(state2, rtindex,
+												 right_state->relids);
+					}
 				}
 				else
 				{
 					if (bms_overlap(nonnullable_rels, right_state->relids))
+					{
 						jointype = JOIN_RIGHT;
+						/* Also report partial reduction in state2 */
+						report_reduced_full_join(state2, rtindex,
+												 left_state->relids);
+					}
 				}
 				break;
 			case JOIN_SEMI:
@@ -2913,8 +2915,8 @@ reduce_outer_joins_pass2(Node *jtnode,
 			j->larg = j->rarg;
 			j->rarg = tmparg;
 			jointype = JOIN_LEFT;
-			right_state = linitial(state->sub_states);
-			left_state = lsecond(state->sub_states);
+			right_state = linitial(state1->sub_states);
+			left_state = lsecond(state1->sub_states);
 		}
 
 		/*
@@ -2945,7 +2947,10 @@ reduce_outer_joins_pass2(Node *jtnode,
 				jointype = JOIN_ANTI;
 		}
 
-		/* Apply the jointype change, if any, to both jointree node and RTE */
+		/*
+		 * Apply the jointype change, if any, to both jointree node and RTE.
+		 * Also, if we changed an RTE to INNER, add its RTI to inner_reduced.
+		 */
 		if (rtindex && jointype != j->jointype)
 		{
 			RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);
@@ -2953,6 +2958,9 @@ reduce_outer_joins_pass2(Node *jtnode,
 			Assert(rte->rtekind == RTE_JOIN);
 			Assert(rte->jointype == j->jointype);
 			rte->jointype = jointype;
+			if (jointype == JOIN_INNER)
+				state2->inner_reduced = bms_add_member(state2->inner_reduced,
+													   rtindex);
 		}
 		j->jointype = jointype;
 
@@ -3025,7 +3033,8 @@ reduce_outer_joins_pass2(Node *jtnode,
 					pass_nonnullable_rels = NULL;
 					pass_forced_null_vars = NIL;
 				}
-				reduce_outer_joins_pass2(j->larg, left_state, root,
+				reduce_outer_joins_pass2(j->larg, left_state,
+										 state2, root,
 										 pass_nonnullable_rels,
 										 pass_forced_null_vars);
 			}
@@ -3044,7 +3053,8 @@ reduce_outer_joins_pass2(Node *jtnode,
 					pass_nonnullable_rels = NULL;
 					pass_forced_null_vars = NIL;
 				}
-				reduce_outer_joins_pass2(j->rarg, right_state, root,
+				reduce_outer_joins_pass2(j->rarg, right_state,
+										 state2, root,
 										 pass_nonnullable_rels,
 										 pass_forced_null_vars);
 			}
@@ -3056,6 +3066,19 @@ reduce_outer_joins_pass2(Node *jtnode,
 			 (int) nodeTag(jtnode));
 }
 
+/* Helper for reduce_outer_joins_pass2 */
+static void
+report_reduced_full_join(reduce_outer_joins_pass2_state *state2,
+						 int rtindex, Relids relids)
+{
+	reduce_outer_joins_partial_state *statep;
+
+	statep = palloc(sizeof(reduce_outer_joins_partial_state));
+	statep->full_join_rti = rtindex;
+	statep->unreduced_side = relids;
+	state2->partial_reduced = lappend(state2->partial_reduced, statep);
+}
+
 
 /*
  * remove_useless_result_rtes
@@ -3097,16 +3120,41 @@ reduce_outer_joins_pass2(Node *jtnode,
 void
 remove_useless_result_rtes(PlannerInfo *root)
 {
+	Relids		dropped_outer_joins = NULL;
 	ListCell   *cell;
 
 	/* Top level of jointree must always be a FromExpr */
 	Assert(IsA(root->parse->jointree, FromExpr));
 	/* Recurse ... */
 	root->parse->jointree = (FromExpr *)
-		remove_useless_results_recurse(root, (Node *) root->parse->jointree);
+		remove_useless_results_recurse(root,
+									   (Node *) root->parse->jointree,
+									   &dropped_outer_joins);
 	/* We should still have a FromExpr */
 	Assert(IsA(root->parse->jointree, FromExpr));
 
+	/*
+	 * If we removed any outer-join nodes from the jointree, run around and
+	 * remove references to those joins as nulling rels.  (There could be such
+	 * references in PHVs that we pulled up out of the original subquery that
+	 * the RESULT rel replaced.  This is kosher on the grounds that we now
+	 * know that such an outer join wouldn't really have nulled anything.)  We
+	 * don't do this during the main recursion, for simplicity and because we
+	 * can handle all such joins in a single pass over the parse tree.
+	 */
+	if (!bms_is_empty(dropped_outer_joins))
+	{
+		root->parse = (Query *)
+			remove_nulling_relids((Node *) root->parse,
+								  dropped_outer_joins,
+								  NULL);
+		/* There could be references in the append_rel_list, too */
+		root->append_rel_list = (List *)
+			remove_nulling_relids((Node *) root->append_rel_list,
+								  dropped_outer_joins,
+								  NULL);
+	}
+
 	/*
 	 * Remove any PlanRowMark referencing an RTE_RESULT RTE.  We obviously
 	 * must do that for any RTE_RESULT that we just removed.  But one for a
@@ -3132,9 +3180,12 @@ remove_useless_result_rtes(PlannerInfo *root)
  *		Recursive guts of remove_useless_result_rtes.
  *
  * This recursively processes the jointree and returns a modified jointree.
+ * In addition, the RT indexes of any removed outer-join nodes are added to
+ * *dropped_outer_joins.
  */
 static Node *
-remove_useless_results_recurse(PlannerInfo *root, Node *jtnode)
+remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
+							   Relids *dropped_outer_joins)
 {
 	Assert(jtnode != NULL);
 	if (IsA(jtnode, RangeTblRef))
@@ -3162,7 +3213,8 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode)
 			int			varno;
 
 			/* Recursively transform child ... */
-			child = remove_useless_results_recurse(root, child);
+			child = remove_useless_results_recurse(root, child,
+												   dropped_outer_joins);
 			/* ... and stick it back into the tree */
 			lfirst(cell) = child;
 
@@ -3211,8 +3263,10 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode)
 		int			varno;
 
 		/* First, recurse */
-		j->larg = remove_useless_results_recurse(root, j->larg);
-		j->rarg = remove_useless_results_recurse(root, j->rarg);
+		j->larg = remove_useless_results_recurse(root, j->larg,
+												 dropped_outer_joins);
+		j->rarg = remove_useless_results_recurse(root, j->rarg,
+												 dropped_outer_joins);
 
 		/* Apply join-type-specific optimization rules */
 		switch (j->jointype)
@@ -3280,6 +3334,8 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode)
 					 !find_dependent_phvs(root, varno)))
 				{
 					remove_result_refs(root, varno, j->larg);
+					*dropped_outer_joins = bms_add_member(*dropped_outer_joins,
+														  j->rtindex);
 					jtnode = j->larg;
 				}
 				break;
@@ -3299,9 +3355,13 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode)
 				 * it'd be OK to just remove the PHV wrapping.  We don't have
 				 * infrastructure for that, but remove_result_refs() will
 				 * relabel them as to be evaluated at the LHS, which is fine.
+				 *
+				 * Also, we don't need to worry about removing traces of the
+				 * join's rtindex, since it hasn't got one.
 				 */
 				if ((varno = get_result_relid(root, j->rarg)) != 0)
 				{
+					Assert(j->rtindex == 0);
 					remove_result_refs(root, varno, j->larg);
 					if (j->quals)
 						jtnode = (Node *)
@@ -3371,7 +3431,7 @@ remove_result_refs(PlannerInfo *root, int varno, Node *newjtloc)
 	{
 		Relids		subrelids;
 
-		subrelids = get_relids_in_jointree(newjtloc, false);
+		subrelids = get_relids_in_jointree(newjtloc, true, false);
 		Assert(!bms_is_empty(subrelids));
 		substitute_phv_relids((Node *) root->parse, varno, subrelids);
 		fix_append_rel_relids(root, varno, subrelids);
@@ -3428,9 +3488,8 @@ find_dependent_phvs_walker(Node *node,
 		context->sublevels_up--;
 		return result;
 	}
-	/* Shouldn't need to handle planner auxiliary nodes here */
+	/* Shouldn't need to handle most planner auxiliary nodes here */
 	Assert(!IsA(node, SpecialJoinInfo));
-	Assert(!IsA(node, AppendRelInfo));
 	Assert(!IsA(node, PlaceHolderInfo));
 	Assert(!IsA(node, MinMaxAggInfo));
 
@@ -3450,10 +3509,17 @@ find_dependent_phvs(PlannerInfo *root, int varno)
 	context.relids = bms_make_singleton(varno);
 	context.sublevels_up = 0;
 
-	return query_tree_walker(root->parse,
-							 find_dependent_phvs_walker,
-							 (void *) &context,
-							 0);
+	if (query_tree_walker(root->parse,
+						  find_dependent_phvs_walker,
+						  (void *) &context,
+						  0))
+		return true;
+	/* The append_rel_list could be populated already, so check it too */
+	if (expression_tree_walker((Node *) root->append_rel_list,
+							   find_dependent_phvs_walker,
+							   (void *) &context))
+		return true;
+	return false;
 }
 
 static bool
@@ -3483,7 +3549,7 @@ find_dependent_phvs_in_jointree(PlannerInfo *root, Node *node, int varno)
 	 * are not marked LATERAL, though, since they couldn't possibly contain
 	 * any cross-references to other RTEs.
 	 */
-	subrelids = get_relids_in_jointree(node, false);
+	subrelids = get_relids_in_jointree(node, false, false);
 	relid = -1;
 	while ((relid = bms_next_member(subrelids, relid)) >= 0)
 	{
@@ -3628,11 +3694,17 @@ fix_append_rel_relids(PlannerInfo *root, int varno, Relids subrelids)
 /*
  * get_relids_in_jointree: get set of RT indexes present in a jointree
  *
- * If include_joins is true, join RT indexes are included; if false,
- * only base rels are included.
+ * Base-relation relids are always included in the result.
+ * If include_outer_joins is true, outer-join RT indexes are included.
+ * If include_inner_joins is true, inner-join RT indexes are included.
+ *
+ * Note that for most purposes in the planner, outer joins are included
+ * in standard relid sets.  Setting include_inner_joins true is only
+ * appropriate for special purposes during subquery flattening.
  */
 Relids
-get_relids_in_jointree(Node *jtnode, bool include_joins)
+get_relids_in_jointree(Node *jtnode, bool include_outer_joins,
+					   bool include_inner_joins)
 {
 	Relids		result = NULL;
 
@@ -3653,18 +3725,34 @@ get_relids_in_jointree(Node *jtnode, bool include_joins)
 		{
 			result = bms_join(result,
 							  get_relids_in_jointree(lfirst(l),
-													 include_joins));
+													 include_outer_joins,
+													 include_inner_joins));
 		}
 	}
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
 
-		result = get_relids_in_jointree(j->larg, include_joins);
+		result = get_relids_in_jointree(j->larg,
+										include_outer_joins,
+										include_inner_joins);
 		result = bms_join(result,
-						  get_relids_in_jointree(j->rarg, include_joins));
-		if (include_joins && j->rtindex)
-			result = bms_add_member(result, j->rtindex);
+						  get_relids_in_jointree(j->rarg,
+												 include_outer_joins,
+												 include_inner_joins));
+		if (j->rtindex)
+		{
+			if (j->jointype == JOIN_INNER)
+			{
+				if (include_inner_joins)
+					result = bms_add_member(result, j->rtindex);
+			}
+			else
+			{
+				if (include_outer_joins)
+					result = bms_add_member(result, j->rtindex);
+			}
+		}
 	}
 	else
 		elog(ERROR, "unrecognized node type: %d",
@@ -3673,7 +3761,7 @@ get_relids_in_jointree(Node *jtnode, bool include_joins)
 }
 
 /*
- * get_relids_for_join: get set of base RT indexes making up a join
+ * get_relids_for_join: get set of base+OJ RT indexes making up a join
  */
 Relids
 get_relids_for_join(Query *query, int joinrelid)
@@ -3684,7 +3772,7 @@ get_relids_for_join(Query *query, int joinrelid)
 										joinrelid);
 	if (!jtnode)
 		elog(ERROR, "could not find join node %d", joinrelid);
-	return get_relids_in_jointree(jtnode, false);
+	return get_relids_in_jointree(jtnode, true, false);
 }
 
 /*
diff --git a/src/backend/optimizer/util/appendinfo.c b/src/backend/optimizer/util/appendinfo.c
index cd45ab4899..61378c8d58 100644
--- a/src/backend/optimizer/util/appendinfo.c
+++ b/src/backend/optimizer/util/appendinfo.c
@@ -228,6 +228,14 @@ adjust_appendrel_attrs_mutator(Node *node,
 		if (var->varlevelsup != 0)
 			return (Node *) var;	/* no changes needed */
 
+		/*
+		 * You might think we need to adjust var->varnullingrels, but that
+		 * shouldn't need any changes.  It will contain outer-join relids,
+		 * while the transformation we are making affects only baserels.
+		 * Below, we just propagate var->varnullingrels into the translated
+		 * Var.  (XXX what to do if translation is not a Var??)
+		 */
+
 		for (cnt = 0; cnt < nappinfos; cnt++)
 		{
 			if (var->varno == appinfos[cnt]->parent_relid)
@@ -255,6 +263,8 @@ adjust_appendrel_attrs_mutator(Node *node,
 				if (newnode == NULL)
 					elog(ERROR, "attribute %d of relation \"%s\" does not exist",
 						 var->varattno, get_rel_name(appinfo->parent_reloid));
+				if (IsA(newnode, Var))
+					((Var *) newnode)->varnullingrels = var->varnullingrels;
 				return newnode;
 			}
 			else if (var->varattno == 0)
@@ -348,6 +358,8 @@ adjust_appendrel_attrs_mutator(Node *node,
 					var = copyObject(ridinfo->rowidvar);
 					/* ... but use the correct relid */
 					var->varno = leaf_relid;
+					/* identity vars shouldn't have nulling rels */
+					Assert(var->varnullingrels == NULL);
 					/* varnosyn in the RowIdentityVarInfo is probably wrong */
 					var->varnosyn = 0;
 					var->varattnosyn = 0;
@@ -392,8 +404,11 @@ adjust_appendrel_attrs_mutator(Node *node,
 														 (void *) context);
 		/* now fix PlaceHolderVar's relid sets */
 		if (phv->phlevelsup == 0)
-			phv->phrels = adjust_child_relids(phv->phrels, context->nappinfos,
-											  context->appinfos);
+		{
+			phv->phrels = adjust_child_relids(phv->phrels,
+											  nappinfos, appinfos);
+			/* as above, we needn't touch phnullingrels */
+		}
 		return (Node *) phv;
 	}
 	/* Shouldn't need to handle planner auxiliary nodes here */
@@ -688,7 +703,11 @@ get_translated_update_targetlist(PlannerInfo *root, Index relid,
 
 /*
  * find_appinfos_by_relids
- * 		Find AppendRelInfo structures for all relations specified by relids.
+ * 		Find AppendRelInfo structures for base relations listed in relids.
+ *
+ * The relids argument is typically a join relation's relids, which can
+ * include outer-join RT indexes in addition to baserels.  We silently
+ * ignore the outer joins.
  *
  * The AppendRelInfos are returned in an array, which can be pfree'd by the
  * caller. *nappinfos is set to the number of entries in the array.
@@ -700,8 +719,9 @@ find_appinfos_by_relids(PlannerInfo *root, Relids relids, int *nappinfos)
 	int			cnt = 0;
 	int			i;
 
-	*nappinfos = bms_num_members(relids);
-	appinfos = (AppendRelInfo **) palloc(sizeof(AppendRelInfo *) * *nappinfos);
+	/* Allocate an array that's certainly big enough */
+	appinfos = (AppendRelInfo **)
+		palloc(sizeof(AppendRelInfo *) * bms_num_members(relids));
 
 	i = -1;
 	while ((i = bms_next_member(relids, i)) >= 0)
@@ -709,10 +729,17 @@ find_appinfos_by_relids(PlannerInfo *root, Relids relids, int *nappinfos)
 		AppendRelInfo *appinfo = root->append_rel_array[i];
 
 		if (!appinfo)
+		{
+			/* Probably i is an OJ index, but let's check */
+			if (find_base_rel_ignore_join(root, i) == NULL)
+				continue;
+			/* It's a base rel, but we lack an append_rel_array entry */
 			elog(ERROR, "child rel %d not found in append_rel_array", i);
+		}
 
 		appinfos[cnt++] = appinfo;
 	}
+	*nappinfos = cnt;
 	return appinfos;
 }
 
@@ -754,6 +781,7 @@ add_row_identity_var(PlannerInfo *root, Var *orig_var,
 	Assert(IsA(orig_var, Var));
 	Assert(orig_var->varno == rtindex);
 	Assert(orig_var->varlevelsup == 0);
+	Assert(orig_var->varnullingrels == NULL);
 
 	/*
 	 * If we're doing non-inherited UPDATE/DELETE/MERGE, there's little need
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index aa584848cf..76e25118f9 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2004,14 +2004,16 @@ is_pseudo_constant_clause_relids(Node *clause, Relids relids)
  * NumRelids
  *		(formerly clause_relids)
  *
- * Returns the number of different relations referenced in 'clause'.
+ * Returns the number of different base relations referenced in 'clause'.
  */
 int
 NumRelids(PlannerInfo *root, Node *clause)
 {
+	int			result;
 	Relids		varnos = pull_varnos(root, clause);
-	int			result = bms_num_members(varnos);
 
+	varnos = bms_del_members(varnos, root->outer_join_rels);
+	result = bms_num_members(varnos);
 	bms_free(varnos);
 	return result;
 }
diff --git a/src/backend/optimizer/util/joininfo.c b/src/backend/optimizer/util/joininfo.c
index 197f20faec..968a5a488e 100644
--- a/src/backend/optimizer/util/joininfo.c
+++ b/src/backend/optimizer/util/joininfo.c
@@ -88,8 +88,8 @@ have_relevant_joinclause(PlannerInfo *root,
  * not depend on context).
  *
  * 'restrictinfo' describes the join clause
- * 'join_relids' is the list of relations participating in the join clause
- *				 (there must be more than one)
+ * 'join_relids' is the set of relations participating in the join clause
+ *				 (some of these could be outer joins)
  */
 void
 add_join_clause_to_rels(PlannerInfo *root,
@@ -101,8 +101,11 @@ add_join_clause_to_rels(PlannerInfo *root,
 	cur_relid = -1;
 	while ((cur_relid = bms_next_member(join_relids, cur_relid)) >= 0)
 	{
-		RelOptInfo *rel = find_base_rel(root, cur_relid);
+		RelOptInfo *rel = find_base_rel_ignore_join(root, cur_relid);
 
+		/* We only need to add the clause to baserels */
+		if (rel == NULL)
+			continue;
 		rel->joininfo = lappend(rel->joininfo, restrictinfo);
 	}
 }
@@ -115,8 +118,8 @@ add_join_clause_to_rels(PlannerInfo *root,
  * discover that a relation need not be joined at all.
  *
  * 'restrictinfo' describes the join clause
- * 'join_relids' is the list of relations participating in the join clause
- *				 (there must be more than one)
+ * 'join_relids' is the set of relations participating in the join clause
+ *				 (some of these could be outer joins)
  */
 void
 remove_join_clause_from_rels(PlannerInfo *root,
@@ -128,7 +131,11 @@ remove_join_clause_from_rels(PlannerInfo *root,
 	cur_relid = -1;
 	while ((cur_relid = bms_next_member(join_relids, cur_relid)) >= 0)
 	{
-		RelOptInfo *rel = find_base_rel(root, cur_relid);
+		RelOptInfo *rel = find_base_rel_ignore_join(root, cur_relid);
+
+		/* We would only have added the clause to baserels */
+		if (rel == NULL)
+			continue;
 
 		/*
 		 * Remove the restrictinfo from the list.  Pointer comparison is
diff --git a/src/backend/optimizer/util/orclauses.c b/src/backend/optimizer/util/orclauses.c
index 493aaa7aed..abc994dbf2 100644
--- a/src/backend/optimizer/util/orclauses.c
+++ b/src/backend/optimizer/util/orclauses.c
@@ -338,6 +338,10 @@ consider_new_or_clause(PlannerInfo *root, RelOptInfo *rel,
 		sjinfo.syn_lefthand = sjinfo.min_lefthand;
 		sjinfo.syn_righthand = sjinfo.min_righthand;
 		sjinfo.jointype = JOIN_INNER;
+		sjinfo.ojrelid = 0;
+		sjinfo.commute_above_l = NULL;
+		sjinfo.commute_above_r = NULL;
+		sjinfo.commute_below = NULL;
 		/* we don't bother trying to make the remaining fields valid */
 		sjinfo.lhs_strict = false;
 		sjinfo.delay_upper_joins = false;
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 4478036bb6..6d76a11c08 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -1307,7 +1307,7 @@ create_append_path(PlannerInfo *root,
 	 * Apply query-wide LIMIT if known and path is for sole base relation.
 	 * (Handling this at this low level is a bit klugy.)
 	 */
-	if (root != NULL && bms_equal(rel->relids, root->all_baserels))
+	if (root != NULL && bms_equal(rel->relids, root->all_query_rels))
 		pathnode->limit_tuples = root->limit_tuples;
 	else
 		pathnode->limit_tuples = -1.0;
@@ -1436,7 +1436,7 @@ create_merge_append_path(PlannerInfo *root,
 	 * Apply query-wide LIMIT if known and path is for sole base relation.
 	 * (Handling this at this low level is a bit klugy.)
 	 */
-	if (bms_equal(rel->relids, root->all_baserels))
+	if (bms_equal(rel->relids, root->all_query_rels))
 		pathnode->limit_tuples = root->limit_tuples;
 	else
 		pathnode->limit_tuples = -1.0;
diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index 72b9977022..af10dbd124 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -23,17 +23,32 @@
 #include "optimizer/planmain.h"
 #include "utils/lsyscache.h"
 
+
+typedef struct contain_placeholder_references_context
+{
+	int			relid;
+	int			sublevels_up;
+} contain_placeholder_references_context;
+
 /* Local functions */
 static void find_placeholders_recurse(PlannerInfo *root, Node *jtnode);
 static void find_placeholders_in_expr(PlannerInfo *root, Node *expr);
+static bool contain_placeholder_references_walker(Node *node,
+												  contain_placeholder_references_context *context);

 /*
  * make_placeholder_expr
  *		Make a PlaceHolderVar for the given expression.
  *
- * phrels is the syntactic location (as a set of baserels) to attribute
+ * phrels is the syntactic location (as a set of relids) to attribute
  * to the expression.
+ *
+ * The caller is responsible for adjusting phlevelsup and phnullingrels
+ * as needed.  Because we do not know here which query level the PHV
+ * will be associated with, it's important that this function touches
+ * only root->glob; messing with other parts of PlannerInfo would be
+ * likely to do the wrong thing.
  */
 PlaceHolderVar *
 make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
@@ -42,8 +57,9 @@ make_placeholder_expr(PlannerInfo *root, Expr *expr, Relids phrels)
 
 	phv->phexpr = expr;
 	phv->phrels = phrels;
+	phv->phnullingrels = NULL;	/* caller may change this later */
 	phv->phid = ++(root->glob->lastPHId);
-	phv->phlevelsup = 0;
+	phv->phlevelsup = 0;		/* caller may change this later */
 
 	return phv;
 }
@@ -92,6 +108,15 @@ find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
 	phinfo->phid = phv->phid;
 	phinfo->ph_var = copyObject(phv);
 
+	/*
+	 * By convention, phinfo->ph_var->phnullingrels is always empty, since the
+	 * PlaceHolderInfo represents the initially-calculated state of the
+	 * PlaceHolderVar.  PlaceHolderVars appearing in the query tree might have
+	 * varying values of phnullingrels, reflecting outer joins applied above
+	 * the calculation level.
+	 */
+	phinfo->ph_var->phnullingrels = NULL;
+
 	/*
 	 * Any referenced rels that are outside the PHV's syntactic scope are
 	 * LATERAL references, which should be included in ph_lateral but not in
@@ -339,6 +364,8 @@ update_placeholder_eval_levels(PlannerInfo *root, SpecialJoinInfo *new_sjinfo)
 												  sjinfo->min_lefthand);
 						eval_at = bms_add_members(eval_at,
 												  sjinfo->min_righthand);
+						if (sjinfo->ojrelid)
+							eval_at = bms_add_member(eval_at, sjinfo->ojrelid);
 						/* we'll need another iteration */
 						found_some = true;
 					}
@@ -413,6 +440,14 @@ add_placeholders_to_base_rels(PlannerInfo *root)
 		{
 			RelOptInfo *rel = find_base_rel(root, varno);
 
+			/*
+			 * As in add_vars_to_targetlist(), a value computed at scan level
+			 * has not yet been nulled by any outer join, so its phnullingrels
+			 * should be empty.
+			 */
+			Assert(phinfo->ph_var->phnullingrels == NULL);
+
+			/* Copying the PHV might be unnecessary here, but be safe */
 			rel->reltarget->exprs = lappend(rel->reltarget->exprs,
 											copyObject(phinfo->ph_var));
 			/* reltarget's cost and width fields will be updated later */
@@ -435,7 +470,8 @@ add_placeholders_to_base_rels(PlannerInfo *root)
  */
 void
 add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
-							RelOptInfo *outer_rel, RelOptInfo *inner_rel)
+							RelOptInfo *outer_rel, RelOptInfo *inner_rel,
+							SpecialJoinInfo *sjinfo)
 {
 	Relids		relids = joinrel->relids;
 	ListCell   *lc;
@@ -466,9 +502,17 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 				if (!bms_is_subset(phinfo->ph_eval_at, outer_rel->relids) &&
 					!bms_is_subset(phinfo->ph_eval_at, inner_rel->relids))
 				{
-					PlaceHolderVar *phv = phinfo->ph_var;
+					/* Copying might be unnecessary here, but be safe */
+					PlaceHolderVar *phv = copyObject(phinfo->ph_var);
 					QualCost	cost;
 
+					/*
+					 * It'll start out not nulled by anything.  Joins above
+					 * this one might add to its phnullingrels later, in much
+					 * the same way as for Vars.
+					 */
+					Assert(phv->phnullingrels == NULL);
+
 					joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
 														phv);
 					cost_qual_eval_node(&cost, (Node *) phv->phexpr, root);
@@ -499,3 +543,74 @@ add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
 		}
 	}
 }
+
+/*
+ * contain_placeholder_references_to
+ *		Detect whether any PlaceHolderVars in the given clause contain
+ *		references to the given relid (typically an OJ relid).
+ *
+ * "Contain" means that there's a use of the relid inside the PHV's
+ * contained expression, so that changing the nullability status of
+ * the rel might change what the PHV computes.
+ *
+ * The code here to cope with upper-level PHVs is likely dead, but keep it
+ * anyway just in case.
+ */
+bool
+contain_placeholder_references_to(PlannerInfo *root, Node *clause,
+								  int relid)
+{
+	contain_placeholder_references_context context;
+
+	/* We can answer quickly in the common case that there's no PHVs at all */
+	if (root->glob->lastPHId == 0)
+		return false;
+	/* Else run the recursive search */
+	context.relid = relid;
+	context.sublevels_up = 0;
+	return contain_placeholder_references_walker(clause, &context);
+}
+
+static bool
+contain_placeholder_references_walker(Node *node,
+									  contain_placeholder_references_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, PlaceHolderVar))
+	{
+		PlaceHolderVar *phv = (PlaceHolderVar *) node;
+
+		/* We should just look through PHVs of other query levels */
+		if (phv->phlevelsup == context->sublevels_up)
+		{
+			/* If phrels matches, we found what we came for */
+			if (bms_is_member(context->relid, phv->phrels))
+				return true;
+
+			/*
+			 * We should not examine phnullingrels: what we are looking for is
+			 * references in the contained expression, not OJs that might null
+			 * the result afterwards.  Also, we don't need to recurse into the
+			 * contained expression, because phrels should adequately
+			 * summarize what's in there.  So we're done here.
+			 */
+			return false;
+		}
+	}
+	else if (IsA(node, Query))
+	{
+		/* Recurse into RTE subquery or not-yet-planned sublink subquery */
+		bool		result;
+
+		context->sublevels_up++;
+		result = query_tree_walker((Query *) node,
+								   contain_placeholder_references_walker,
+								   context,
+								   0);
+		context->sublevels_up--;
+		return result;
+	}
+	return expression_tree_walker(node, contain_placeholder_references_walker,
+								  context);
+}
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 0a5632699d..34de0029bd 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -28,6 +28,7 @@
 #include "optimizer/plancat.h"
 #include "optimizer/restrictinfo.h"
 #include "optimizer/tlist.h"
+#include "rewrite/rewriteManip.h"
 #include "parser/parse_relation.h"
 #include "utils/hsearch.h"
 #include "utils/lsyscache.h"
@@ -40,7 +41,9 @@ typedef struct JoinHashEntry
 } JoinHashEntry;
 
 static void build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
-								RelOptInfo *input_rel);
+								RelOptInfo *input_rel,
+								SpecialJoinInfo *sjinfo,
+								bool can_null);
 static List *build_joinrel_restrictlist(PlannerInfo *root,
 										RelOptInfo *joinrel,
 										RelOptInfo *outer_rel,
@@ -48,8 +51,10 @@ static List *build_joinrel_restrictlist(PlannerInfo *root,
 static void build_joinrel_joinlist(RelOptInfo *joinrel,
 								   RelOptInfo *outer_rel,
 								   RelOptInfo *inner_rel);
-static List *subbuild_joinrel_restrictlist(RelOptInfo *joinrel,
-										   List *joininfo_list,
+static List *subbuild_joinrel_restrictlist(PlannerInfo *root,
+										   RelOptInfo *joinrel,
+										   RelOptInfo *input_rel,
+										   Relids both_input_relids,
 										   List *new_restrictlist);
 static List *subbuild_joinrel_joinlist(RelOptInfo *joinrel,
 									   List *joininfo_list,
@@ -57,10 +62,12 @@ static List *subbuild_joinrel_joinlist(RelOptInfo *joinrel,
 static void set_foreign_rel_properties(RelOptInfo *joinrel,
 									   RelOptInfo *outer_rel, RelOptInfo *inner_rel);
 static void add_join_rel(PlannerInfo *root, RelOptInfo *joinrel);
-static void build_joinrel_partition_info(RelOptInfo *joinrel,
+static void build_joinrel_partition_info(PlannerInfo *root,
+										 RelOptInfo *joinrel,
 										 RelOptInfo *outer_rel, RelOptInfo *inner_rel,
-										 List *restrictlist, JoinType jointype);
-static bool have_partkey_equi_join(RelOptInfo *joinrel,
+										 SpecialJoinInfo *sjinfo,
+										 List *restrictlist);
+static bool have_partkey_equi_join(PlannerInfo *root, RelOptInfo *joinrel,
 								   RelOptInfo *rel1, RelOptInfo *rel2,
 								   JoinType jointype, List *restrictlist);
 static int	match_expr_to_partition_keys(Expr *expr, RelOptInfo *rel,
@@ -373,7 +380,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 
 /*
  * find_base_rel
- *	  Find a base or other relation entry, which must already exist.
+ *	  Find a base or otherrel relation entry, which must already exist.
  */
 RelOptInfo *
 find_base_rel(PlannerInfo *root, int relid)
@@ -394,6 +401,44 @@ find_base_rel(PlannerInfo *root, int relid)
 	return NULL;				/* keep compiler quiet */
 }
 
+/*
+ * find_base_rel_ignore_join
+ *	  Find a base or otherrel relation entry, which must already exist.
+ *
+ * Unlike find_base_rel, if relid references an outer join then this
+ * will return NULL rather than raising an error.  This is convenient
+ * for callers that must deal with relid sets including both base and
+ * outer joins.
+ */
+RelOptInfo *
+find_base_rel_ignore_join(PlannerInfo *root, int relid)
+{
+	Assert(relid > 0);
+
+	if (relid < root->simple_rel_array_size)
+	{
+		RelOptInfo *rel;
+		RangeTblEntry *rte;
+
+		rel = root->simple_rel_array[relid];
+		if (rel)
+			return rel;
+
+		/*
+		 * We could just return NULL here, but for debugging purposes it seems
+		 * best to actually verify that the relid is an outer join and not
+		 * something weird.
+		 */
+		rte = root->simple_rte_array[relid];
+		if (rte && rte->rtekind == RTE_JOIN && rte->jointype != JOIN_INNER)
+			return NULL;
+	}
+
+	elog(ERROR, "no relation entry for relid %d", relid);
+
+	return NULL;				/* keep compiler quiet */
+}
+
 /*
  * build_join_rel_hash
  *	  Construct the auxiliary hash table for join relations.
@@ -692,9 +737,11 @@ build_join_rel(PlannerInfo *root,
 	 * and inner rels we first try to build it from.  But the contents should
 	 * be the same regardless.
 	 */
-	build_joinrel_tlist(root, joinrel, outer_rel);
-	build_joinrel_tlist(root, joinrel, inner_rel);
-	add_placeholders_to_joinrel(root, joinrel, outer_rel, inner_rel);
+	build_joinrel_tlist(root, joinrel, outer_rel, sjinfo,
+						(sjinfo->jointype == JOIN_FULL));
+	build_joinrel_tlist(root, joinrel, inner_rel, sjinfo,
+						(sjinfo->jointype != JOIN_INNER));
+	add_placeholders_to_joinrel(root, joinrel, outer_rel, inner_rel, sjinfo);
 
 	/*
 	 * add_placeholders_to_joinrel also took care of adding the ph_lateral
@@ -726,8 +773,8 @@ build_join_rel(PlannerInfo *root,
 	joinrel->has_eclass_joins = has_relevant_eclass_joinclause(root, joinrel);
 
 	/* Store the partition information. */
-	build_joinrel_partition_info(joinrel, outer_rel, inner_rel, restrictlist,
-								 sjinfo->jointype);
+	build_joinrel_partition_info(root, joinrel, outer_rel, inner_rel, sjinfo,
+								 restrictlist);
 
 	/*
 	 * Set estimates of the joinrel's size.
@@ -783,16 +830,14 @@ build_join_rel(PlannerInfo *root,
  * 'parent_joinrel' is the RelOptInfo representing the join between parent
  *		relations. Some of the members of new RelOptInfo are produced by
  *		translating corresponding members of this RelOptInfo
- * 'sjinfo': child-join context info
  * 'restrictlist': list of RestrictInfo nodes that apply to this particular
  *		pair of joinable relations
- * 'jointype' is the join type (inner, left, full, etc)
+ * 'sjinfo': child join's join-type details
  */
 RelOptInfo *
 build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 					 RelOptInfo *inner_rel, RelOptInfo *parent_joinrel,
-					 List *restrictlist, SpecialJoinInfo *sjinfo,
-					 JoinType jointype)
+					 List *restrictlist, SpecialJoinInfo *sjinfo)
 {
 	RelOptInfo *joinrel = makeNode(RelOptInfo);
 	AppendRelInfo **appinfos;
@@ -806,6 +851,8 @@ build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 
 	joinrel->reloptkind = RELOPT_OTHER_JOINREL;
 	joinrel->relids = bms_union(outer_rel->relids, inner_rel->relids);
+	if (sjinfo->ojrelid != 0)
+		joinrel->relids = bms_add_member(joinrel->relids, sjinfo->ojrelid);
 	joinrel->rows = 0;
 	/* cheap startup cost is interesting iff not all tuples to be retrieved */
 	joinrel->consider_startup = (root->tuple_fraction > 0);
@@ -892,8 +939,8 @@ build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 	joinrel->has_eclass_joins = parent_joinrel->has_eclass_joins;
 
 	/* Is the join between partitions itself partitioned? */
-	build_joinrel_partition_info(joinrel, outer_rel, inner_rel, restrictlist,
-								 jointype);
+	build_joinrel_partition_info(root, joinrel, outer_rel, inner_rel, sjinfo,
+								 restrictlist);
 
 	/* Child joinrel is parallel safe if parent is parallel safe. */
 	joinrel->consider_parallel = parent_joinrel->consider_parallel;
@@ -975,10 +1022,41 @@ min_join_parameterization(PlannerInfo *root,
  *
  * We also compute the expected width of the join's output, making use
  * of data that was cached at the baserel level by set_rel_width().
+ *
+ * Pass can_null as true if the join is an outer join that can null Vars
+ * from this input relation.  If so, we will (normally) add the join's relid
+ * to the nulling bitmaps of Vars and PHVs bubbled up from the input.
+ *
+ * When forming an outer join's target list, special handling is needed
+ * in case the outer join was commuted with another one per outer join
+ * identity 3 (see optimizer/README).  We must take steps to ensure that
+ * the output Vars have the same nulling bitmaps that they would if the
+ * two joins had been done in syntactic order; else they won't match Vars
+ * appearing higher in the query tree.  We need to do two things:
+ *
+ * First, sjinfo->commute_above_r is added to the nulling bitmaps of RHS Vars.
+ * This takes care of the case where we implement
+ *		A leftjoin (B leftjoin C on (Pbc)) on (Pab)
+ * as
+ *		(A leftjoin B on (Pab)) leftjoin C on (Pbc)
+ * The C columns emitted by the B/C join need to be shown as nulled by both
+ * the B/C and A/B joins, even though they've not traversed the A/B join.
+ * (If the joins haven't been commuted, we are adding the nullingrel bits
+ * prematurely; but that's okay because the C columns can't be referenced
+ * between here and the upper join.)
+ *
+ * Second, if a RHS Var has any of the relids in sjinfo->commute_above_l
+ * already set in its nulling bitmap, then we *don't* add sjinfo->ojrelid
+ * to its nulling bitmap (but we do still add commute_above_r).  This takes
+ * care of the reverse transformation: if the original syntax was
+ *		(A leftjoin B on (Pab)) leftjoin C on (Pbc)
+ * then the now-upper A/B join must not mark C columns as nulled by itself.
  */
 static void
 build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
-					RelOptInfo *input_rel)
+					RelOptInfo *input_rel,
+					SpecialJoinInfo *sjinfo,
+					bool can_null)
 {
 	Relids		relids = joinrel->relids;
 	ListCell   *vars;
@@ -998,7 +1076,24 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 			/* Is it still needed above this joinrel? */
 			if (bms_nonempty_difference(phinfo->ph_needed, relids))
 			{
-				/* Yup, add it to the output */
+				/*
+				 * Yup, add it to the output.  If this join potentially nulls
+				 * this input, we have to update the PHV's phnullingrels,
+				 * which means making a copy.
+				 */
+				if (can_null)
+				{
+					phv = copyObject(phv);
+					/* See comments above to understand this logic */
+					if (sjinfo->ojrelid != 0 &&
+						!bms_overlap(phv->phnullingrels, sjinfo->commute_above_l))
+						phv->phnullingrels = bms_add_member(phv->phnullingrels,
+															sjinfo->ojrelid);
+					if (sjinfo->commute_above_r)
+						phv->phnullingrels = bms_add_members(phv->phnullingrels,
+															 sjinfo->commute_above_r);
+				}
+
 				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
 													phv);
 				/* Bubbling up the precomputed result has cost zero */
@@ -1022,9 +1117,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 			RowIdentityVarInfo *ridinfo = (RowIdentityVarInfo *)
 			list_nth(root->row_identity_vars, var->varattno - 1);
 
-			joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
-												var);
-			/* Vars have cost zero, so no need to adjust reltarget->cost */
+			/* Update reltarget width estimate from RowIdentityVarInfo */
 			joinrel->reltarget->width += ridinfo->rowidwidth;
 		}
 		else
@@ -1037,15 +1130,35 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
 
 			/* Is it still needed above this joinrel? */
 			ndx = var->varattno - baserel->min_attr;
-			if (bms_nonempty_difference(baserel->attr_needed[ndx], relids))
-			{
-				/* Yup, add it to the output */
-				joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
-													var);
-				/* Vars have cost zero, so no need to adjust reltarget->cost */
-				joinrel->reltarget->width += baserel->attr_widths[ndx];
-			}
+			if (!bms_nonempty_difference(baserel->attr_needed[ndx], relids))
+				continue;		/* nope, skip it */
+
+			/* Update reltarget width estimate from baserel's attr_widths */
+			joinrel->reltarget->width += baserel->attr_widths[ndx];
+		}
+
+		/*
+		 * Add the Var to the output.  If this join potentially nulls this
+		 * input, we have to update the Var's varnullingrels, which means
+		 * making a copy.
+		 */
+		if (can_null)
+		{
+			var = copyObject(var);
+			/* See comments above to understand this logic */
+			if (sjinfo->ojrelid != 0 &&
+				!bms_overlap(var->varnullingrels, sjinfo->commute_above_l))
+				var->varnullingrels = bms_add_member(var->varnullingrels,
+													 sjinfo->ojrelid);
+			if (sjinfo->commute_above_r)
+				var->varnullingrels = bms_add_members(var->varnullingrels,
+													  sjinfo->commute_above_r);
 		}
+
+		joinrel->reltarget->exprs = lappend(joinrel->reltarget->exprs,
+											var);
+
+		/* Vars have cost zero, so no need to adjust reltarget->cost */
 	}
 }
 
@@ -1064,7 +1177,7 @@ build_joinrel_tlist(PlannerInfo *root, RelOptInfo *joinrel,
  *	  is not handled in the sub-relations, so it depends on which
  *	  sub-relations are considered.
  *
- *	  If a join clause from an input relation refers to base rels still not
+ *	  If a join clause from an input relation refers to base+OJ rels still not
  *	  present in the joinrel, then it is still a join clause for the joinrel;
  *	  we put it into the joininfo list for the joinrel.  Otherwise,
  *	  the clause is now a restrict clause for the joined relation, and we
@@ -1098,14 +1211,19 @@ build_joinrel_restrictlist(PlannerInfo *root,
 						   RelOptInfo *inner_rel)
 {
 	List	   *result;
+	Relids		both_input_relids;
+
+	both_input_relids = bms_union(outer_rel->relids, inner_rel->relids);
 
 	/*
 	 * Collect all the clauses that syntactically belong at this level,
 	 * eliminating any duplicates (important since we will see many of the
 	 * same clauses arriving from both input relations).
 	 */
-	result = subbuild_joinrel_restrictlist(joinrel, outer_rel->joininfo, NIL);
-	result = subbuild_joinrel_restrictlist(joinrel, inner_rel->joininfo, result);
+	result = subbuild_joinrel_restrictlist(root, joinrel, outer_rel,
+										   both_input_relids, NIL);
+	result = subbuild_joinrel_restrictlist(root, joinrel, inner_rel,
+										   both_input_relids, result);
 
 	/*
 	 * Add on any clauses derived from EquivalenceClasses.  These cannot be
@@ -1140,24 +1258,63 @@ build_joinrel_joinlist(RelOptInfo *joinrel,
 }
 
 static List *
-subbuild_joinrel_restrictlist(RelOptInfo *joinrel,
-							  List *joininfo_list,
+subbuild_joinrel_restrictlist(PlannerInfo *root,
+							  RelOptInfo *joinrel,
+							  RelOptInfo *input_rel,
+							  Relids both_input_relids,
 							  List *new_restrictlist)
 {
 	ListCell   *l;
 
-	foreach(l, joininfo_list)
+	foreach(l, input_rel->joininfo)
 	{
 		RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
 
 		if (bms_is_subset(rinfo->required_relids, joinrel->relids))
 		{
 			/*
-			 * This clause becomes a restriction clause for the joinrel, since
-			 * it refers to no outside rels.  Add it to the list, being
-			 * careful to eliminate duplicates. (Since RestrictInfo nodes in
-			 * different joinlists will have been multiply-linked rather than
-			 * copied, pointer equality should be a sufficient test.)
+			 * This clause should become a restriction clause for the joinrel,
+			 * since it refers to no outside rels.  However, if it's a clone
+			 * clause then it might be too late to evaluate it, so we have to
+			 * check.  (If it is too late, just ignore the clause, taking it
+			 * on faith that another clone was or will be selected.)  Clone
+			 * clauses should always be outer-join clauses, so we compare
+			 * against both_input_relids.
+			 */
+			if (rinfo->has_clone || rinfo->is_clone)
+			{
+				Assert(!RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids));
+				if (!bms_is_subset(rinfo->required_relids, both_input_relids))
+					continue;
+				if (!clause_is_computable_at(root, rinfo->clause_relids,
+											 both_input_relids))
+					continue;
+			}
+			else
+			{
+				/*
+				 * For non-clone clauses, we just Assert it's OK.  These might
+				 * be either join or filter clauses.
+				 */
+#ifdef USE_ASSERT_CHECKING
+				if (RINFO_IS_PUSHED_DOWN(rinfo, joinrel->relids))
+					Assert(clause_is_computable_at(root, rinfo->clause_relids,
+												   joinrel->relids));
+				else
+				{
+					Assert(bms_is_subset(rinfo->required_relids,
+										 both_input_relids));
+					Assert(clause_is_computable_at(root, rinfo->clause_relids,
+												   both_input_relids));
+				}
+#endif
+			}
+
+			/*
+			 * OK, so add it to the list, being careful to eliminate
+			 * duplicates.  (Since RestrictInfo nodes in different joinlists
+			 * will have been multiply-linked rather than copied, pointer
+			 * equality should be a sufficient test.)
 			 */
 			new_restrictlist = list_append_unique_ptr(new_restrictlist, rinfo);
 		}
@@ -1664,9 +1821,10 @@ find_param_path_info(RelOptInfo *rel, Relids required_outer)
  *		partitioned join relation.
  */
 static void
-build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
-							 RelOptInfo *inner_rel, List *restrictlist,
-							 JoinType jointype)
+build_joinrel_partition_info(PlannerInfo *root,
+							 RelOptInfo *joinrel, RelOptInfo *outer_rel,
+							 RelOptInfo *inner_rel, SpecialJoinInfo *sjinfo,
+							 List *restrictlist)
 {
 	PartitionScheme part_scheme;
 
@@ -1692,8 +1850,8 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 		!outer_rel->consider_partitionwise_join ||
 		!inner_rel->consider_partitionwise_join ||
 		outer_rel->part_scheme != inner_rel->part_scheme ||
-		!have_partkey_equi_join(joinrel, outer_rel, inner_rel,
-								jointype, restrictlist))
+		!have_partkey_equi_join(root, joinrel, outer_rel, inner_rel,
+								sjinfo->jointype, restrictlist))
 	{
 		Assert(!IS_PARTITIONED_REL(joinrel));
 		return;
@@ -1717,7 +1875,8 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
 	 * child-join relations of the join relation in try_partitionwise_join().
 	 */
 	joinrel->part_scheme = part_scheme;
-	set_joinrel_partition_key_exprs(joinrel, outer_rel, inner_rel, jointype);
+	set_joinrel_partition_key_exprs(joinrel, outer_rel, inner_rel,
+									sjinfo->jointype);
 
 	/*
 	 * Set the consider_partitionwise_join flag.
@@ -1735,7 +1894,7 @@ build_joinrel_partition_info(RelOptInfo *joinrel, RelOptInfo *outer_rel,
  * partition keys.
  */
 static bool
-have_partkey_equi_join(RelOptInfo *joinrel,
+have_partkey_equi_join(PlannerInfo *root, RelOptInfo *joinrel,
 					   RelOptInfo *rel1, RelOptInfo *rel2,
 					   JoinType jointype, List *restrictlist)
 {
@@ -1800,6 +1959,24 @@ have_partkey_equi_join(RelOptInfo *joinrel,
 		 */
 		strict_op = op_strict(opexpr->opno);
 
+		/*
+		 * Vars appearing in the relation's partition keys will not have any
+		 * varnullingrels, but those in expr1 and expr2 will if we're above
+		 * outer joins that could null the respective rels.  It's okay to
+		 * match anyway, if the join operator is strict.
+		 */
+		if (strict_op)
+		{
+			if (bms_overlap(rel1->relids, root->outer_join_rels))
+				expr1 = (Expr *) remove_nulling_relids((Node *) expr1,
+													   root->outer_join_rels,
+													   NULL);
+			if (bms_overlap(rel2->relids, root->outer_join_rels))
+				expr2 = (Expr *) remove_nulling_relids((Node *) expr2,
+													   root->outer_join_rels,
+													   NULL);
+		}
+
 		/*
 		 * Only clauses referencing the partition keys are useful for
 		 * partitionwise join.
@@ -2012,7 +2189,12 @@ set_joinrel_partition_key_exprs(RelOptInfo *joinrel,
 				 * partitionwise nesting of any outer join.)  We assume no
 				 * type coercions are needed to make the coalesce expressions,
 				 * since columns of different types won't have gotten
-				 * classified as the same PartitionScheme.
+				 * classified as the same PartitionScheme.  Note that we
+				 * intentionally leave out the varnullingrels decoration that
+				 * would ordinarily appear on the Vars inside these
+				 * CoalesceExprs, because have_partkey_equi_join will strip
+				 * varnullingrels from the expressions it will compare to the
+				 * partexprs.
 				 */
 				foreach(lc, list_concat_copy(outer_expr, outer_null_expr))
 				{
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index 0c3878a805..d6dd8307ec 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -53,6 +53,10 @@ static Expr *make_sub_restrictinfos(PlannerInfo *root,
  * required_relids can be NULL, in which case it defaults to the actual clause
  * contents (i.e., clause_relids).
  *
+ * Note that there aren't options to set the has_clone and is_clone flags:
+ * we always initialize those to false.  There's just one place that wants
+ * something different, so making all callers pass them seems inconvenient.
+ *
  * We initialize fields that depend only on the given subexpression, leaving
  * others that depend on context (or may never be needed at all) to be filled
  * later.
@@ -116,12 +120,15 @@ make_restrictinfo_internal(PlannerInfo *root,
 						   Relids nullable_relids)
 {
 	RestrictInfo *restrictinfo = makeNode(RestrictInfo);
+	Relids		baserels;
 
 	restrictinfo->clause = clause;
 	restrictinfo->orclause = orclause;
 	restrictinfo->is_pushed_down = is_pushed_down;
 	restrictinfo->outerjoin_delayed = outerjoin_delayed;
 	restrictinfo->pseudoconstant = pseudoconstant;
+	restrictinfo->has_clone = false;	/* may get set by caller */
+	restrictinfo->is_clone = false; /* may get set by caller */
 	restrictinfo->can_join = false; /* may get set below */
 	restrictinfo->security_level = security_level;
 	restrictinfo->outer_relids = outer_relids;
@@ -187,6 +194,20 @@ make_restrictinfo_internal(PlannerInfo *root,
 	else
 		restrictinfo->required_relids = restrictinfo->clause_relids;
 
+	/*
+	 * Count the number of base rels appearing in clause_relids.  To do this,
+	 * we just delete rels mentioned in root->outer_join_rels and count the
+	 * survivors.  Because we are called during deconstruct_jointree which is
+	 * the same tree walk that populates outer_join_rels, this is a little bit
+	 * unsafe-looking; but it should be fine because the recursion in
+	 * deconstruct_jointree should already have visited any outer join that
+	 * could be mentioned in this clause.
+	 */
+	baserels = bms_difference(restrictinfo->clause_relids,
+							  root->outer_join_rels);
+	restrictinfo->num_base_rels = bms_num_members(baserels);
+	bms_free(baserels);
+
 	/*
 	 * Fill in all the cacheable fields with "not yet set" markers. None of
 	 * these will be computed until/unless needed.  Note in particular that we
@@ -497,6 +518,58 @@ extract_actual_join_clauses(List *restrictinfo_list,
 	}
 }
 
+/*
+ * clause_is_computable_at
+ *		Test whether a clause is computable at a given evaluation level.
+ *
+ * There are two conditions for whether an expression can actually be
+ * evaluated at a given join level: the evaluation context must include
+ * all the relids (both base and OJ) used by the expression, and we must
+ * not have already evaluated any outer joins that null Vars/PHVs of the
+ * expression and are not listed in their nullingrels.
+ *
+ * This function checks the second condition; we assume the caller already
+ * saw to the first one.
+ *
+ * For speed reasons, we don't individually examine each Var/PHV of the
+ * expression, but just look at the overall clause_relids (the union of the
+ * varnos and varnullingrels).  This could give a misleading answer if the
+ * Vars of a given varno don't all have the same varnullingrels; but that
+ * really shouldn't happen within a single scalar expression or RestrictInfo
+ * clause.  Despite that, this is still annoyingly expensive :-(
+ */
+bool
+clause_is_computable_at(PlannerInfo *root,
+						Relids clause_relids,
+						Relids eval_relids)
+{
+	ListCell   *lc;
+
+	/* Nothing to do if no outer joins have been performed yet. */
+	if (!bms_overlap(eval_relids, root->outer_join_rels))
+		return true;
+
+	foreach(lc, root->join_info_list)
+	{
+		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
+
+		/* Ignore outer joins that are not yet performed. */
+		if (!bms_is_member(sjinfo->ojrelid, eval_relids))
+			continue;
+
+		/* OK if clause lists it (we assume all Vars in it agree). */
+		if (bms_is_member(sjinfo->ojrelid, clause_relids))
+			continue;
+
+		/* Else, trouble if clause mentions any nullable Vars. */
+		if (bms_overlap(clause_relids, sjinfo->min_righthand) ||
+			(sjinfo->jointype == JOIN_FULL &&
+			 bms_overlap(clause_relids, sjinfo->min_lefthand)))
+			return false;		/* doesn't work */
+	}
+
+	return true;				/* OK */
+}
 
 /*
  * join_clause_is_movable_to
@@ -522,6 +595,12 @@ extract_actual_join_clauses(List *restrictinfo_list,
  * Also, the join clause must not use any relations that have LATERAL
  * references to the target relation, since we could not put such rels on
  * the outer side of a nestloop with the target relation.
+ *
+ * Also, we reject is_clone versions of outer-join clauses.  This has the
+ * effect of preventing us from generating variant parameterized paths
+ * that differ only in which outer joins null the parameterization rel(s).
+ * Generating one path from the minimally-parameterized has_clone version
+ * is sufficient.
  */
 bool
 join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
@@ -542,6 +621,10 @@ join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
 	if (bms_overlap(baserel->lateral_referencers, rinfo->clause_relids))
 		return false;
 
+	/* Ignore clones, too */
+	if (rinfo->is_clone)
+		return false;
+
 	return true;
 }
 
@@ -587,6 +670,9 @@ join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
  * moved for some valid set of outer rels, so we don't have the benefit of
  * relying on prior checks for lateral-reference validity.
  *
+ * Likewise, we don't check is_clone here: rejecting the inappropriate
+ * variants of a cloned clause must be handled upstream.
+ *
  * Note: if this returns true, it means that the clause could be moved to
  * this join relation, but that doesn't mean that this is the lowest join
  * it could be moved to.  Caller may need to make additional calls to verify
diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index 09cc7d6f51..b65de54cf8 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -88,6 +88,9 @@ static Relids alias_relid_set(Query *query, Relids relids);
  *		Create a set of all the distinct varnos present in a parsetree.
  *		Only varnos that reference level-zero rtable entries are considered.
  *
+ * The result includes outer-join relids mentioned in Var.varnullingrels and
+ * PlaceHolderVar.phnullingrels fields in the parsetree.
+ *
  * "root" can be passed as NULL if it is not necessary to process
  * PlaceHolderVars.
  *
@@ -153,7 +156,11 @@ pull_varnos_walker(Node *node, pull_varnos_context *context)
 		Var		   *var = (Var *) node;
 
 		if (var->varlevelsup == context->sublevels_up)
+		{
 			context->varnos = bms_add_member(context->varnos, var->varno);
+			context->varnos = bms_add_members(context->varnos,
+											  var->varnullingrels);
+		}
 		return false;
 	}
 	if (IsA(node, CurrentOfExpr))
@@ -244,6 +251,14 @@ pull_varnos_walker(Node *node, pull_varnos_context *context)
 				context->varnos = bms_join(context->varnos,
 										   newevalat);
 			}
+
+			/*
+			 * In all three cases, include phnullingrels in the result.  We
+			 * don't worry about possibly needing to translate it, because
+			 * appendrels only translate varnos of baserels, not outer joins.
+			 */
+			context->varnos = bms_add_members(context->varnos,
+											  phv->phnullingrels);
 			return false;		/* don't recurse into expression */
 		}
 	}
diff --git a/src/backend/utils/adt/selfuncs.c b/src/backend/utils/adt/selfuncs.c
index 4e4888dde4..fe37e65af0 100644
--- a/src/backend/utils/adt/selfuncs.c
+++ b/src/backend/utils/adt/selfuncs.c
@@ -2206,7 +2206,7 @@ rowcomparesel(PlannerInfo *root,
 	else
 	{
 		/*
-		 * Otherwise, it's a join if there's more than one relation used.
+		 * Otherwise, it's a join if there's more than one base relation used.
 		 */
 		is_join_clause = (NumRelids(root, (Node *) opargs) > 1);
 	}
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 0909420615..583af844d0 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -254,6 +254,20 @@ struct PlannerInfo
 	 */
 	Relids		all_baserels;
 
+	/*
+	 * outer_join_rels is a Relids set of all outer-join relids in the query.
+	 * This is computed in deconstruct_jointree.
+	 */
+	Relids		outer_join_rels;
+
+	/*
+	 * all_query_rels is a Relids set of all base relids and outer join relids
+	 * (but not "other" relids) in the query.  This is the Relids identifier
+	 * of the final join we need to form.  This is computed in
+	 * deconstruct_jointree.
+	 */
+	Relids		all_query_rels;
+
 	/*
 	 * nullable_baserels is a Relids set of base relids that are nullable by
 	 * some outer join in the jointree; these are rels that are potentially
@@ -590,9 +604,10 @@ typedef struct PartitionSchemeData *PartitionScheme;
  * or the output of a sub-SELECT or function that appears in the range table.
  * In either case it is uniquely identified by an RT index.  A "joinrel"
  * is the joining of two or more base rels.  A joinrel is identified by
- * the set of RT indexes for its component baserels.  We create RelOptInfo
- * nodes for each baserel and joinrel, and store them in the PlannerInfo's
- * simple_rel_array and join_rel_list respectively.
+ * the set of RT indexes for its component baserels, along with RT indexes
+ * for any outer joins it has computed.  We create RelOptInfo nodes for each
+ * baserel and joinrel, and store them in the PlannerInfo's simple_rel_array
+ * and join_rel_list respectively.
  *
  * Note that there is only one joinrel for any given set of component
  * baserels, no matter what order we assemble them in; so an unordered
@@ -631,8 +646,10 @@ typedef struct PartitionSchemeData *PartitionScheme;
  * Parts of this data structure are specific to various scan and join
  * mechanisms.  It didn't seem worth creating new node types for them.
  *
- *		relids - Set of base-relation identifiers; it is a base relation
- *				if there is just one, a join relation if more than one
+ *		relids - Set of relation identifiers (RT indexes).  This is a base
+ *				 relation if there is just one, a join relation if more;
+ *				 in the join case, RT indexes of any outer joins formed
+ *				 at or below this join are included along with baserels
  *		rows - estimated number of tuples in the relation after restriction
  *			   clauses have been applied (ie, output rows of a plan for it)
  *		consider_startup - true if there is any value in keeping plain paths for
@@ -844,7 +861,7 @@ typedef struct RelOptInfo
 	RelOptKind	reloptkind;
 
 	/*
-	 * all relations included in this RelOptInfo; set of base relids
+	 * all relations included in this RelOptInfo; set of base + OJ relids
 	 * (rangetable indexes)
 	 */
 	Relids		relids;
@@ -2314,17 +2331,17 @@ typedef struct LimitPath
  * If a restriction clause references a single base relation, it will appear
  * in the baserestrictinfo list of the RelOptInfo for that base rel.
  *
- * If a restriction clause references more than one base rel, it will
+ * If a restriction clause references more than one base+OJ relation, it will
  * appear in the joininfo list of every RelOptInfo that describes a strict
- * subset of the base rels mentioned in the clause.  The joininfo lists are
+ * subset of the relations mentioned in the clause.  The joininfo lists are
  * used to drive join tree building by selecting plausible join candidates.
  * The clause cannot actually be applied until we have built a join rel
- * containing all the base rels it references, however.
+ * containing all the relations it references, however.
  *
- * When we construct a join rel that includes all the base rels referenced
+ * When we construct a join rel that includes all the relations referenced
  * in a multi-relation restriction clause, we place that clause into the
  * joinrestrictinfo lists of paths for the join rel, if neither left nor
- * right sub-path includes all base rels referenced in the clause.  The clause
+ * right sub-path includes all relations referenced in the clause.  The clause
  * will be applied at that join level, and will not propagate any further up
  * the join tree.  (Note: the "predicate migration" code was once intended to
  * push restriction clauses up and down the plan tree based on evaluation
@@ -2345,12 +2362,14 @@ typedef struct LimitPath
  * or join to enforce that all members of each EquivalenceClass are in fact
  * equal in all rows emitted by the scan or join.
  *
- * When dealing with outer joins we have to be very careful about pushing qual
- * clauses up and down the tree.  An outer join's own JOIN/ON conditions must
- * be evaluated exactly at that join node, unless they are "degenerate"
- * conditions that reference only Vars from the nullable side of the join.
- * Quals appearing in WHERE or in a JOIN above the outer join cannot be pushed
- * down below the outer join, if they reference any nullable Vars.
+ * The clause_relids field lists the base plus outer-join RT indexes that
+ * actually appear in the clause.  required_relids lists the minimum set of
+ * relids needed to evaluate the clause; while this is often equal to
+ * clause_relids, it can be more.  We will add relids to required_relids when
+ * we need to force an outer join ON clause to be evaluated exactly at the
+ * level of the outer join, which is true except when it is a "degenerate"
+ * condition that references only Vars from the nullable side of the join.
+ *
  * RestrictInfo nodes contain a flag to indicate whether a qual has been
  * pushed down to a lower level than its original syntactic placement in the
  * join tree would suggest.  If an outer join prevents us from pushing a qual
@@ -2435,6 +2454,12 @@ typedef struct LimitPath
  * or merge or hash join clause, so it's of no interest to large parts of
  * the planner.
  *
+ * When we generate multiple versions of a clause so as to have versions
+ * that will work after commuting some left joins per outer join identity 3,
+ * we mark the one with the fewest nullingrels bits with has_clone = true,
+ * and the rest with is_clone = true.  This allows proper filtering of
+ * these redundant clauses, so that we apply only one version of them.
+ *
  * When join clauses are generated from EquivalenceClasses, there may be
  * several equally valid ways to enforce join equivalence, of which we need
  * apply only one.  We mark clauses of this kind by setting parent_ec to
@@ -2469,16 +2494,23 @@ typedef struct RestrictInfo
 	/* see comment above */
 	bool		pseudoconstant pg_node_attr(equal_ignore);
 
+	/* see comment above */
+	bool		has_clone;
+	bool		is_clone;
+
 	/* true if known to contain no leaked Vars */
 	bool		leakproof pg_node_attr(equal_ignore);
 
-	/* to indicate if clause contains any volatile functions. */
+	/* indicates if clause contains any volatile functions */
 	VolatileFunctionStatus has_volatile pg_node_attr(equal_ignore);
 
 	/* see comment above */
 	Index		security_level;
 
-	/* The set of relids (varnos) actually referenced in the clause: */
+	/* number of base rels in clause_relids */
+	int			num_base_rels pg_node_attr(equal_ignore);
+
+	/* The relids (varnos+varnullingrels) actually referenced in the clause: */
 	Relids		clause_relids pg_node_attr(equal_ignore);
 
 	/* The set of relids required to evaluate the clause: */
@@ -2682,20 +2714,49 @@ typedef struct PlaceHolderVar
  * We make SpecialJoinInfos for FULL JOINs even though there is no flexibility
  * of planning for them, because this simplifies make_join_rel()'s API.
  *
- * min_lefthand and min_righthand are the sets of base relids that must be
- * available on each side when performing the special join.  lhs_strict is
- * true if the special join's condition cannot succeed when the LHS variables
- * are all NULL (this means that an outer join can commute with upper-level
- * outer joins even if it appears in their RHS).  We don't bother to set
- * lhs_strict for FULL JOINs, however.
- *
+ * min_lefthand and min_righthand are the sets of base+OJ relids that must be
+ * available on each side when performing the special join.
  * It is not valid for either min_lefthand or min_righthand to be empty sets;
  * if they were, this would break the logic that enforces join order.
  *
- * syn_lefthand and syn_righthand are the sets of base relids that are
+ * syn_lefthand and syn_righthand are the sets of base+OJ relids that are
  * syntactically below this special join.  (These are needed to help compute
  * min_lefthand and min_righthand for higher joins.)
  *
+ * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
+ * the inputs to make it a LEFT JOIN.  So the allowed values of jointype
+ * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
+ *
+ * ojrelid is the RT index of the join RTE representing this outer join,
+ * if there is one.  It is zero when jointype is INNER or SEMI, and can be
+ * zero for jointype ANTI (if the join was transformed from a SEMI join).
+ * One use for this field is that when constructing the output targetlist of a
+ * join relation that implements this OJ, we add ojrelid to the varnullingrels
+ * and phnullingrels fields of nullable (RHS) output columns, so that the
+ * output Vars and PlaceHolderVars correctly reflect the nulling that has
+ * potentially happened to them.
+ *
+ * commute_above_l is filled with the relids of syntactically-higher outer
+ * joins that have been found to commute with this one per outer join identity
+ * 3 (see optimizer/README), when this join is in the LHS of the upper join
+ * (so, this is the lower join in the first form of the identity).
+ *
+ * commute_above_r is filled with the relids of syntactically-higher outer
+ * joins that have been found to commute with this one per outer join identity
+ * 3, when this join is in the RHS of the upper join (so, this is the lower
+ * join in the second form of the identity).
+ *
+ * commute_below is filled with the relids of syntactically-lower outer joins
+ * that have been found to commute with this one per outer join identity 3.
+ * (We need not record which side they are on, since that can be determined
+ * by seeing whether the lower join's relid appears in syn_lefthand or
+ * syn_righthand.)
+ *
+ * lhs_strict is true if the special join's condition cannot succeed when the
+ * LHS variables are all NULL (this means that an outer join can commute with
+ * upper-level outer joins even if it appears in their RHS).  We don't bother
+ * to set lhs_strict for FULL JOINs, however.
+ *
  * delay_upper_joins is set true if we detect a pushed-down clause that has
  * to be evaluated after this join is formed (because it references the RHS).
  * Any outer joins that have such a clause and this join in their RHS cannot
@@ -2710,10 +2771,6 @@ typedef struct PlaceHolderVar
  * join planning; but it's helpful to have it available during planning of
  * parameterized table scans, so we store it in the SpecialJoinInfo structs.)
  *
- * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
- * the inputs to make it a LEFT JOIN.  So the allowed values of jointype
- * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
- *
  * For purposes of join selectivity estimation, we create transient
  * SpecialJoinInfo structures for regular inner joins; so it is possible
  * to have jointype == JOIN_INNER in such a structure, even though this is
@@ -2733,11 +2790,15 @@ struct SpecialJoinInfo
 	pg_node_attr(no_read)
 
 	NodeTag		type;
-	Relids		min_lefthand;	/* base relids in minimum LHS for join */
-	Relids		min_righthand;	/* base relids in minimum RHS for join */
-	Relids		syn_lefthand;	/* base relids syntactically within LHS */
-	Relids		syn_righthand;	/* base relids syntactically within RHS */
+	Relids		min_lefthand;	/* base+OJ relids in minimum LHS for join */
+	Relids		min_righthand;	/* base+OJ relids in minimum RHS for join */
+	Relids		syn_lefthand;	/* base+OJ relids syntactically within LHS */
+	Relids		syn_righthand;	/* base+OJ relids syntactically within RHS */
 	JoinType	jointype;		/* always INNER, LEFT, FULL, SEMI, or ANTI */
+	Index		ojrelid;		/* outer join's RT index; 0 if none */
+	Relids		commute_above_l;	/* commuting OJs above this one, if LHS */
+	Relids		commute_above_r;	/* commuting OJs above this one, if RHS */
+	Relids		commute_below;	/* commuting OJs below this one */
 	bool		lhs_strict;		/* joinclause is strict for some LHS rel */
 	bool		delay_upper_joins;	/* can't commute with upper RHS */
 	/* Remaining fields are set only for JOIN_SEMI jointype: */
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 02305ef902..8c05cafc8a 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -304,6 +304,7 @@ extern void expand_planner_arrays(PlannerInfo *root, int add_size);
 extern RelOptInfo *build_simple_rel(PlannerInfo *root, int relid,
 									RelOptInfo *parent);
 extern RelOptInfo *find_base_rel(PlannerInfo *root, int relid);
+extern RelOptInfo *find_base_rel_ignore_join(PlannerInfo *root, int relid);
 extern RelOptInfo *find_join_rel(PlannerInfo *root, Relids relids);
 extern RelOptInfo *build_join_rel(PlannerInfo *root,
 								  Relids joinrelids,
@@ -335,6 +336,6 @@ extern ParamPathInfo *find_param_path_info(RelOptInfo *rel,
 extern RelOptInfo *build_child_join_rel(PlannerInfo *root,
 										RelOptInfo *outer_rel, RelOptInfo *inner_rel,
 										RelOptInfo *parent_joinrel, List *restrictlist,
-										SpecialJoinInfo *sjinfo, JoinType jointype);
+										SpecialJoinInfo *sjinfo);
 
 #endif							/* PATHNODE_H */
diff --git a/src/include/optimizer/placeholder.h b/src/include/optimizer/placeholder.h
index 7367dca1e8..31e1578e82 100644
--- a/src/include/optimizer/placeholder.h
+++ b/src/include/optimizer/placeholder.h
@@ -27,6 +27,9 @@ extern void update_placeholder_eval_levels(PlannerInfo *root,
 extern void fix_placeholder_input_needed_levels(PlannerInfo *root);
 extern void add_placeholders_to_base_rels(PlannerInfo *root);
 extern void add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
-										RelOptInfo *outer_rel, RelOptInfo *inner_rel);
+										RelOptInfo *outer_rel, RelOptInfo *inner_rel,
+										SpecialJoinInfo *sjinfo);
+extern bool contain_placeholder_references_to(PlannerInfo *root, Node *clause,
+											  int relid);
 
 #endif							/* PLACEHOLDER_H */
diff --git a/src/include/optimizer/prep.h b/src/include/optimizer/prep.h
index 452b92ad55..54fd61c9c3 100644
--- a/src/include/optimizer/prep.h
+++ b/src/include/optimizer/prep.h
@@ -29,7 +29,8 @@ extern void pull_up_subqueries(PlannerInfo *root);
 extern void flatten_simple_union_all(PlannerInfo *root);
 extern void reduce_outer_joins(PlannerInfo *root);
 extern void remove_useless_result_rtes(PlannerInfo *root);
-extern Relids get_relids_in_jointree(Node *jtnode, bool include_joins);
+extern Relids get_relids_in_jointree(Node *jtnode, bool include_outer_joins,
+									 bool include_inner_joins);
 extern Relids get_relids_for_join(Query *query, int joinrelid);
 
 /*
diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index a47fccc2ed..c79bb420e4 100644
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -41,6 +41,9 @@ extern void extract_actual_join_clauses(List *restrictinfo_list,
 										Relids joinrelids,
 										List **joinquals,
 										List **otherquals);
+extern bool clause_is_computable_at(PlannerInfo *root,
+									Relids clause_relids,
+									Relids eval_relids);
 extern bool join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel);
 extern bool join_clause_is_movable_into(RestrictInfo *rinfo,
 										Relids currentrelids,
commit 7bcf9dbe7b0ce47701729bc190deeb6fcbad99c4
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:35:26 2023 -0500

    Detect duplicated pushed-down conditions using RestrictInfo ID numbers.
    
    create_nestloop_path needs to identify which candidates for join
    restriction quals were already enforced in the parameterized inner
    path.  Currently we do that by relying on join_clause_is_movable_into
    to give consistent answers, but that is not working very well with
    variant clauses generated to satisfy outer join identity 3.  We may
    have a clause that (correctly) shows the outer-side Var as nulled by
    a previous outer join, which makes it dependent on the nestloop outer
    side having included that join, so that it appears to not be pushable
    into a parameterized path that uses the un-nulled version of that Var.
    Nonetheless, the cloned clause *is* redundant and we don't want
    to check it again.
    
    This patch offers a somewhat brute-force solution, which is to assign
    serial numbers to RestrictInfo nodes, then check for redundancy using
    serial number match rather than trusting join_clause_is_movable_into.
    The variant-clause problem can be solved by allowing clauses to share
    a serial number when we know that they are equivalent.  Both the
    outer-join variant generator and equivclass.c need to be in on that
    trick in order to handle all cases that were handled well before.
    
    It'd be nicer if we could continue to trust join_clause_is_movable_into
    for this, but on the other hand this mechanism does provide a much more
    concrete, harder-to-break way of verifying that we already enforced
    (some version of) a qual.  Any failure mode would almost certainly
    be in the safe direction of enforcing a qual redundantly, which is
    not a claim that the existing method can make.
    
    This patch results in two changes to the core regression test outputs:
    
    * One query in join.sql changes to a different join order.  Examining
    the cost estimates that are normally not shown, the new order is
    estimated as very slightly faster, so this seems like an improvement.
    I'm not quite sure why the old code did not find this join order.
    
    * Some of the queries in partition_join.sql revert equivalence-clause
    ordering back to what it was before a5fc46414.  That's probably a
    consequence of investigating parameterized paths in a different order
    than before.  Anyway, it's visibly harmless.

diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index bfde80e8a4..6cbb72a672 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -35,7 +35,8 @@
 
 static EquivalenceMember *add_eq_member(EquivalenceClass *ec,
 										Expr *expr, Relids relids, Relids nullable_relids,
-										bool is_child, Oid datatype);
+										EquivalenceMember *parent,
+										Oid datatype);
 static bool is_exprlist_member(Expr *node, List *exprs);
 static void generate_base_implied_equalities_const(PlannerInfo *root,
 												   EquivalenceClass *ec);
@@ -400,7 +401,7 @@ process_equivalence(PlannerInfo *root,
 	{
 		/* Case 3: add item2 to ec1 */
 		em2 = add_eq_member(ec1, item2, item2_relids, item2_nullable_relids,
-							false, item2_type);
+							NULL, item2_type);
 		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
 		ec1->ec_below_outer_join |= below_outer_join;
 		ec1->ec_min_security = Min(ec1->ec_min_security,
@@ -418,7 +419,7 @@ process_equivalence(PlannerInfo *root,
 	{
 		/* Case 3: add item1 to ec2 */
 		em1 = add_eq_member(ec2, item1, item1_relids, item1_nullable_relids,
-							false, item1_type);
+							NULL, item1_type);
 		ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
 		ec2->ec_below_outer_join |= below_outer_join;
 		ec2->ec_min_security = Min(ec2->ec_min_security,
@@ -452,9 +453,9 @@ process_equivalence(PlannerInfo *root,
 		ec->ec_max_security = restrictinfo->security_level;
 		ec->ec_merged = NULL;
 		em1 = add_eq_member(ec, item1, item1_relids, item1_nullable_relids,
-							false, item1_type);
+							NULL, item1_type);
 		em2 = add_eq_member(ec, item2, item2_relids, item2_nullable_relids,
-							false, item2_type);
+							NULL, item2_type);
 
 		root->eq_classes = lappend(root->eq_classes, ec);
 
@@ -544,7 +545,7 @@ canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
  */
 static EquivalenceMember *
 add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
-			  Relids nullable_relids, bool is_child, Oid datatype)
+			  Relids nullable_relids, EquivalenceMember *parent, Oid datatype)
 {
 	EquivalenceMember *em = makeNode(EquivalenceMember);
 
@@ -552,8 +553,9 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
 	em->em_relids = relids;
 	em->em_nullable_relids = nullable_relids;
 	em->em_is_const = false;
-	em->em_is_child = is_child;
+	em->em_is_child = (parent != NULL);
 	em->em_datatype = datatype;
+	em->em_parent = parent;
 
 	if (bms_is_empty(relids))
 	{
@@ -565,12 +567,12 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
 		 * get_eclass_for_sort_expr() has to work harder.  We put the tests
 		 * there not here to save cycles in the equivalence case.
 		 */
-		Assert(!is_child);
+		Assert(!parent);
 		em->em_is_const = true;
 		ec->ec_has_const = true;
 		/* it can't affect ec_relids */
 	}
-	else if (!is_child)			/* child members don't add to ec_relids */
+	else if (!parent)			/* child members don't add to ec_relids */
 	{
 		ec->ec_relids = bms_add_members(ec->ec_relids, relids);
 	}
@@ -723,7 +725,7 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 	nullable_relids = bms_intersect(nullable_relids, expr_relids);
 
 	newem = add_eq_member(newec, copyObject(expr), expr_relids,
-						  nullable_relids, false, opcintype);
+						  nullable_relids, NULL, opcintype);
 
 	/*
 	 * add_eq_member doesn't check for volatile functions, set-returning
@@ -1821,6 +1823,7 @@ create_join_clause(PlannerInfo *root,
 				   EquivalenceClass *parent_ec)
 {
 	RestrictInfo *rinfo;
+	RestrictInfo *parent_rinfo = NULL;
 	ListCell   *lc;
 	MemoryContext oldcontext;
 
@@ -1865,6 +1868,20 @@ create_join_clause(PlannerInfo *root,
 	 */
 	oldcontext = MemoryContextSwitchTo(root->planner_cxt);
 
+	/*
+	 * If either EM is a child, recursively create the corresponding
+	 * parent-to-parent clause, so that we can duplicate its rinfo_serial.
+	 */
+	if (leftem->em_is_child || rightem->em_is_child)
+	{
+		EquivalenceMember *leftp = leftem->em_parent ? leftem->em_parent : leftem;
+		EquivalenceMember *rightp = rightem->em_parent ? rightem->em_parent : rightem;
+
+		parent_rinfo = create_join_clause(root, ec, opno,
+										  leftp, rightp,
+										  parent_ec);
+	}
+
 	rinfo = build_implied_join_equality(root,
 										opno,
 										ec->ec_collation,
@@ -1876,6 +1893,10 @@ create_join_clause(PlannerInfo *root,
 												  rightem->em_nullable_relids),
 										ec->ec_min_security);
 
+	/* If it's a child clause, copy the parent's rinfo_serial */
+	if (parent_rinfo)
+		rinfo->rinfo_serial = parent_rinfo->rinfo_serial;
+
 	/* Mark the clause as redundant, or not */
 	rinfo->parent_ec = parent_ec;
 
@@ -2691,7 +2712,7 @@ add_child_rel_equivalences(PlannerInfo *root,
 
 				(void) add_eq_member(cur_ec, child_expr,
 									 new_relids, new_nullable_relids,
-									 true, cur_em->em_datatype);
+									 cur_em, cur_em->em_datatype);
 
 				/* Record this EC index for the child rel */
 				child_rel->eclass_indexes = bms_add_member(child_rel->eclass_indexes, i);
@@ -2832,7 +2853,7 @@ add_child_join_rel_equivalences(PlannerInfo *root,
 
 				(void) add_eq_member(cur_ec, child_expr,
 									 new_relids, new_nullable_relids,
-									 true, cur_em->em_datatype);
+									 cur_em, cur_em->em_datatype);
 			}
 		}
 	}
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 7bd654a77e..7db8291549 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -1889,6 +1889,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
 		Relids		joins_below;
 		Relids		joins_so_far;
 		List	   *quals;
+		int			save_last_rinfo_serial;
 		ListCell   *lc;
 
 		/*
@@ -1927,6 +1928,16 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
 												   joins_below,
 												   NULL);
 
+		/*
+		 * Each time we produce RestrictInfo(s) from these quals, reset the
+		 * last_rinfo_serial counter, so that the RestrictInfos for the "same"
+		 * qual condition get identical serial numbers.  (This relies on the
+		 * fact that we're not changing the qual list in any way that'd affect
+		 * the number of RestrictInfos built from it.) This'll allow us to
+		 * detect duplicative qual usage later.
+		 */
+		save_last_rinfo_serial = root->last_rinfo_serial;
+
 		joins_so_far = NULL;
 		foreach(lc, jtitems)
 		{
@@ -1964,6 +1975,9 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
 				continue;
 			}
 
+			/* Reset serial counter for this version of the quals */
+			root->last_rinfo_serial = save_last_rinfo_serial;
+
 			/*
 			 * When we are looking at joins above sjinfo, we are envisioning
 			 * pushing sjinfo to above othersj, so add othersj's nulling bit
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 8a472bce0c..12fe442980 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -627,6 +627,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	root->multiexpr_params = NIL;
 	root->eq_classes = NIL;
 	root->ec_merging_done = false;
+	root->last_rinfo_serial = 0;
 	root->all_result_relids =
 		parse->resultRelation ? bms_make_singleton(parse->resultRelation) : NULL;
 	root->leaf_result_relids = NULL;	/* we'll find out leaf-ness later */
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 029172333e..a5380361bf 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -992,6 +992,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->multiexpr_params = NIL;
 	subroot->eq_classes = NIL;
 	subroot->ec_merging_done = false;
+	subroot->last_rinfo_serial = 0;
 	subroot->all_result_relids = NULL;
 	subroot->leaf_result_relids = NULL;
 	subroot->append_rel_list = NIL;
diff --git a/src/backend/optimizer/util/appendinfo.c b/src/backend/optimizer/util/appendinfo.c
index 61378c8d58..dba895ccc4 100644
--- a/src/backend/optimizer/util/appendinfo.c
+++ b/src/backend/optimizer/util/appendinfo.c
@@ -427,7 +427,7 @@ adjust_appendrel_attrs_mutator(Node *node,
 		RestrictInfo *oldinfo = (RestrictInfo *) node;
 		RestrictInfo *newinfo = makeNode(RestrictInfo);
 
-		/* Copy all flat-copiable fields */
+		/* Copy all flat-copiable fields, notably including rinfo_serial */
 		memcpy(newinfo, oldinfo, sizeof(RestrictInfo));
 
 		/* Recursively fix the clause itself */
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index 6d76a11c08..f2bf68d33b 100644
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -2442,12 +2442,12 @@ create_nestloop_path(PlannerInfo *root,
 	 * restrict_clauses that are due to be moved into the inner path.  We have
 	 * to do this now, rather than postpone the work till createplan time,
 	 * because the restrict_clauses list can affect the size and cost
-	 * estimates for this path.
+	 * estimates for this path.  We detect such clauses by checking for serial
+	 * number match to clauses already enforced in the inner path.
 	 */
 	if (bms_overlap(inner_req_outer, outer_path->parent->relids))
 	{
-		Relids		inner_and_outer = bms_union(inner_path->parent->relids,
-												inner_req_outer);
+		Bitmapset  *enforced_serials = get_param_path_clause_serials(inner_path);
 		List	   *jclauses = NIL;
 		ListCell   *lc;
 
@@ -2455,9 +2455,7 @@ create_nestloop_path(PlannerInfo *root,
 		{
 			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
 
-			if (!join_clause_is_movable_into(rinfo,
-											 inner_path->parent->relids,
-											 inner_and_outer))
+			if (!bms_is_member(rinfo->rinfo_serial, enforced_serials))
 				jclauses = lappend(jclauses, rinfo);
 		}
 		restrict_clauses = jclauses;
@@ -4298,6 +4296,7 @@ do { \
 		new_ppi->ppi_rows = old_ppi->ppi_rows;
 		new_ppi->ppi_clauses = old_ppi->ppi_clauses;
 		ADJUST_CHILD_ATTRS(new_ppi->ppi_clauses);
+		new_ppi->ppi_serials = bms_copy(old_ppi->ppi_serials);
 		rel->ppilist = lappend(rel->ppilist, new_ppi);
 
 		MemoryContextSwitchTo(oldcontext);
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 34de0029bd..ebfb4ddd12 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -1476,6 +1476,7 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
 	ParamPathInfo *ppi;
 	Relids		joinrelids;
 	List	   *pclauses;
+	Bitmapset  *pserials;
 	double		rows;
 	ListCell   *lc;
 
@@ -1518,6 +1519,15 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
 															required_outer,
 															baserel));
 
+	/* Compute set of serial numbers of the enforced clauses */
+	pserials = NULL;
+	foreach(lc, pclauses)
+	{
+		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+		pserials = bms_add_member(pserials, rinfo->rinfo_serial);
+	}
+
 	/* Estimate the number of rows returned by the parameterized scan */
 	rows = get_parameterized_baserel_size(root, baserel, pclauses);
 
@@ -1526,6 +1536,7 @@ get_baserel_parampathinfo(PlannerInfo *root, RelOptInfo *baserel,
 	ppi->ppi_req_outer = required_outer;
 	ppi->ppi_rows = rows;
 	ppi->ppi_clauses = pclauses;
+	ppi->ppi_serials = pserials;
 	baserel->ppilist = lappend(baserel->ppilist, ppi);
 
 	return ppi;
@@ -1751,6 +1762,7 @@ get_joinrel_parampathinfo(PlannerInfo *root, RelOptInfo *joinrel,
 	ppi->ppi_req_outer = required_outer;
 	ppi->ppi_rows = rows;
 	ppi->ppi_clauses = NIL;
+	ppi->ppi_serials = NULL;
 	joinrel->ppilist = lappend(joinrel->ppilist, ppi);
 
 	return ppi;
@@ -1789,6 +1801,7 @@ get_appendrel_parampathinfo(RelOptInfo *appendrel, Relids required_outer)
 	ppi->ppi_req_outer = required_outer;
 	ppi->ppi_rows = 0;
 	ppi->ppi_clauses = NIL;
+	ppi->ppi_serials = NULL;
 	appendrel->ppilist = lappend(appendrel->ppilist, ppi);
 
 	return ppi;
@@ -1814,6 +1827,100 @@ find_param_path_info(RelOptInfo *rel, Relids required_outer)
 	return NULL;
 }
 
+/*
+ * get_param_path_clause_serials
+ *		Given a parameterized Path, return the set of pushed-down clauses
+ *		(identified by rinfo_serial numbers) enforced within the Path.
+ */
+Bitmapset *
+get_param_path_clause_serials(Path *path)
+{
+	if (path->param_info == NULL)
+		return NULL;			/* not parameterized */
+	if (IsA(path, NestPath) ||
+		IsA(path, MergePath) ||
+		IsA(path, HashPath))
+	{
+		/*
+		 * For a join path, combine clauses enforced within either input path
+		 * with those enforced as joinrestrictinfo in this path.  Note that
+		 * joinrestrictinfo may include some non-pushed-down clauses, but for
+		 * current purposes it's okay if we include those in the result. (To
+		 * be more careful, we could check for clause_relids overlapping the
+		 * path parameterization, but it's not worth the cycles for now.)
+		 */
+		JoinPath   *jpath = (JoinPath *) path;
+		Bitmapset  *pserials;
+		ListCell   *lc;
+
+		pserials = NULL;
+		pserials = bms_add_members(pserials,
+								   get_param_path_clause_serials(jpath->outerjoinpath));
+		pserials = bms_add_members(pserials,
+								   get_param_path_clause_serials(jpath->innerjoinpath));
+		foreach(lc, jpath->joinrestrictinfo)
+		{
+			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
+
+			pserials = bms_add_member(pserials, rinfo->rinfo_serial);
+		}
+		return pserials;
+	}
+	else if (IsA(path, AppendPath))
+	{
+		/*
+		 * For an appendrel, take the intersection of the sets of clauses
+		 * enforced in each input path.
+		 */
+		AppendPath *apath = (AppendPath *) path;
+		Bitmapset  *pserials;
+		ListCell   *lc;
+
+		pserials = NULL;
+		foreach(lc, apath->subpaths)
+		{
+			Path	   *subpath = (Path *) lfirst(lc);
+			Bitmapset  *subserials;
+
+			subserials = get_param_path_clause_serials(subpath);
+			if (lc == list_head(apath->subpaths))
+				pserials = bms_copy(subserials);
+			else
+				pserials = bms_int_members(pserials, subserials);
+		}
+		return pserials;
+	}
+	else if (IsA(path, MergeAppendPath))
+	{
+		/* Same as AppendPath case */
+		MergeAppendPath *apath = (MergeAppendPath *) path;
+		Bitmapset  *pserials;
+		ListCell   *lc;
+
+		pserials = NULL;
+		foreach(lc, apath->subpaths)
+		{
+			Path	   *subpath = (Path *) lfirst(lc);
+			Bitmapset  *subserials;
+
+			subserials = get_param_path_clause_serials(subpath);
+			if (lc == list_head(apath->subpaths))
+				pserials = bms_copy(subserials);
+			else
+				pserials = bms_int_members(pserials, subserials);
+		}
+		return pserials;
+	}
+	else
+	{
+		/*
+		 * Otherwise, it's a baserel path and we can use the
+		 * previously-computed set of serial numbers.
+		 */
+		return path->param_info->ppi_serials;
+	}
+}
+
 /*
  * build_joinrel_partition_info
  *		Checks if the two relations being joined can use partitionwise join
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index d6dd8307ec..1350f011a6 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -208,6 +208,11 @@ make_restrictinfo_internal(PlannerInfo *root,
 	restrictinfo->num_base_rels = bms_num_members(baserels);
 	bms_free(baserels);
 
+	/*
+	 * Label this RestrictInfo with a fresh serial number.
+	 */
+	restrictinfo->rinfo_serial = ++(root->last_rinfo_serial);
+
 	/*
 	 * Fill in all the cacheable fields with "not yet set" markers. None of
 	 * these will be computed until/unless needed.  Note in particular that we
@@ -371,7 +376,7 @@ commute_restrictinfo(RestrictInfo *rinfo, Oid comm_op)
 	 * ... and adjust those we need to change.  Note in particular that we can
 	 * preserve any cached selectivity or cost estimates, since those ought to
 	 * be the same for the new clause.  Likewise we can keep the source's
-	 * parent_ec.
+	 * parent_ec.  It's also important that we keep the same rinfo_serial.
 	 */
 	result->clause = (Expr *) newclause;
 	result->left_relids = rinfo->right_relids;
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 583af844d0..630a044089 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -344,6 +344,9 @@ struct PlannerInfo
 	/* list of SpecialJoinInfos */
 	List	   *join_info_list;
 
+	/* counter for assigning RestrictInfo serial numbers */
+	int			last_rinfo_serial;
+
 	/*
 	 * all_result_relids is empty for SELECT, otherwise it contains at least
 	 * parse->resultRelation.  For UPDATE/DELETE/MERGE across an inheritance
@@ -1390,6 +1393,8 @@ typedef struct EquivalenceMember
 	bool		em_is_const;	/* expression is pseudoconstant? */
 	bool		em_is_child;	/* derived version for a child relation? */
 	Oid			em_datatype;	/* the "nominal type" used by the opfamily */
+	/* if em_is_child is true, this links to corresponding EM for top parent */
+	struct EquivalenceMember *em_parent pg_node_attr(read_write_ignore);
 } EquivalenceMember;
 
 /*
@@ -1496,7 +1501,13 @@ typedef struct PathTarget
  * Note: ppi_clauses is only used in ParamPathInfos for base relation paths;
  * in join cases it's NIL because the set of relevant clauses varies depending
  * on how the join is formed.  The relevant clauses will appear in each
- * parameterized join path's joinrestrictinfo list, instead.
+ * parameterized join path's joinrestrictinfo list, instead.  ParamPathInfos
+ * for append relations don't bother with this, either.
+ *
+ * ppi_serials is the set of rinfo_serial numbers for quals that are enforced
+ * by this path.  As with ppi_clauses, it's only maintained for baserels.
+ * (We could construct it on-the-fly from ppi_clauses, but it seems better
+ * to materialize a copy.)
  */
 typedef struct ParamPathInfo
 {
@@ -1507,6 +1518,7 @@ typedef struct ParamPathInfo
 	Relids		ppi_req_outer;	/* rels supplying parameters used by path */
 	Cardinality ppi_rows;		/* estimated number of result tuples */
 	List	   *ppi_clauses;	/* join clauses available from outer rels */
+	Bitmapset  *ppi_serials;	/* set of rinfo_serial for enforced quals */
 } ParamPathInfo;

@@ -2535,6 +2547,25 @@ typedef struct RestrictInfo
 	 */
 	Expr	   *orclause pg_node_attr(equal_ignore);
 
+	/*----------
+	 * Serial number of this RestrictInfo.  This is unique within the current
+	 * PlannerInfo context, with a few critical exceptions:
+	 * 1. When we generate multiple clones of the same qual condition to
+	 * cope with outer join identity 3, all the clones get the same serial
+	 * number.  This reflects that we only want to apply one of them in any
+	 * given plan.
+	 * 2. If we manufacture a commuted version of a qual to use as an index
+	 * condition, it copies the original's rinfo_serial, since it is in
+	 * practice the same condition.
+	 * 3. RestrictInfos made for a child relation copy their parent's
+	 * rinfo_serial.  Likewise, when an EquivalenceClass makes a derived
+	 * equality clause for a child relation, it copies the rinfo_serial of
+	 * the matching equality clause for the parent.  This allows detection
+	 * of redundant pushed-down equality clauses.
+	 *----------
+	 */
+	int			rinfo_serial;
+
 	/*
 	 * Generating EquivalenceClass.  This field is NULL unless clause is
 	 * potentially redundant.
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 8c05cafc8a..69be701b16 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -333,6 +333,7 @@ extern ParamPathInfo *get_appendrel_parampathinfo(RelOptInfo *appendrel,
 												  Relids required_outer);
 extern ParamPathInfo *find_param_path_info(RelOptInfo *rel,
 										   Relids required_outer);
+extern Bitmapset *get_param_path_clause_serials(Path *path);
 extern RelOptInfo *build_child_join_rel(PlannerInfo *root,
 										RelOptInfo *outer_rel, RelOptInfo *inner_rel,
 										RelOptInfo *parent_joinrel, List *restrictlist,
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index c2b85d2795..360d87e1ed 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -2335,17 +2335,17 @@ select a.f1, b.f1, t.thousand, t.tenthous from
   (select sum(f1)+1 as f1 from int4_tbl i4a) a,
   (select sum(f1) as f1 from int4_tbl i4b) b
 where b.f1 = t.thousand and a.f1 = b.f1 and (a.f1+b.f1+999) = t.tenthous;
-                                                      QUERY PLAN                                                       
------------------------------------------------------------------------------------------------------------------------
+                                                   QUERY PLAN                                                    
+-----------------------------------------------------------------------------------------------------------------
  Nested Loop
-   ->  Aggregate
-         ->  Seq Scan on int4_tbl i4b
    ->  Nested Loop
          Join Filter: ((sum(i4b.f1)) = ((sum(i4a.f1) + 1)))
          ->  Aggregate
                ->  Seq Scan on int4_tbl i4a
-         ->  Index Only Scan using tenk1_thous_tenthous on tenk1 t
-               Index Cond: ((thousand = (sum(i4b.f1))) AND (tenthous = ((((sum(i4a.f1) + 1)) + (sum(i4b.f1))) + 999)))
+         ->  Aggregate
+               ->  Seq Scan on int4_tbl i4b
+   ->  Index Only Scan using tenk1_thous_tenthous on tenk1 t
+         Index Cond: ((thousand = (sum(i4b.f1))) AND (tenthous = ((((sum(i4a.f1) + 1)) + (sum(i4b.f1))) + 999)))
 (9 rows)
 
 select a.f1, b.f1, t.thousand, t.tenthous from
diff --git a/src/test/regress/expected/partition_join.out b/src/test/regress/expected/partition_join.out
index c0ff13fb82..e18641ab92 100644
--- a/src/test/regress/expected/partition_join.out
+++ b/src/test/regress/expected/partition_join.out
@@ -304,7 +304,7 @@ SELECT t1.* FROM prt1 t1 WHERE t1.a IN (SELECT t2.b FROM prt2 t2 WHERE t2.a = 0)
                      ->  Seq Scan on prt2_p2 t2_2
                            Filter: (a = 0)
          ->  Nested Loop Semi Join
-               Join Filter: (t2_3.b = t1_3.a)
+               Join Filter: (t1_3.a = t2_3.b)
                ->  Seq Scan on prt1_p3 t1_3
                      Filter: (b = 0)
                ->  Materialize
@@ -601,7 +601,7 @@ SELECT t1.a, t1.c, t2.b, t2.c, t3.a + t3.b, t3.c FROM prt1 t1, prt2 t2, prt1_e t
    Sort Key: t1.a
    ->  Append
          ->  Nested Loop
-               Join Filter: (((t3_1.a + t3_1.b) / 2) = t1_1.a)
+               Join Filter: (t1_1.a = ((t3_1.a + t3_1.b) / 2))
                ->  Hash Join
                      Hash Cond: (t2_1.b = t1_1.a)
                      ->  Seq Scan on prt2_p1 t2_1
@@ -611,7 +611,7 @@ SELECT t1.a, t1.c, t2.b, t2.c, t3.a + t3.b, t3.c FROM prt1 t1, prt2 t2, prt1_e t
                ->  Index Scan using iprt1_e_p1_ab2 on prt1_e_p1 t3_1
                      Index Cond: (((a + b) / 2) = t2_1.b)
          ->  Nested Loop
-               Join Filter: (((t3_2.a + t3_2.b) / 2) = t1_2.a)
+               Join Filter: (t1_2.a = ((t3_2.a + t3_2.b) / 2))
                ->  Hash Join
                      Hash Cond: (t2_2.b = t1_2.a)
                      ->  Seq Scan on prt2_p2 t2_2
@@ -621,7 +621,7 @@ SELECT t1.a, t1.c, t2.b, t2.c, t3.a + t3.b, t3.c FROM prt1 t1, prt2 t2, prt1_e t
                ->  Index Scan using iprt1_e_p2_ab2 on prt1_e_p2 t3_2
                      Index Cond: (((a + b) / 2) = t2_2.b)
          ->  Nested Loop
-               Join Filter: (((t3_3.a + t3_3.b) / 2) = t1_3.a)
+               Join Filter: (t1_3.a = ((t3_3.a + t3_3.b) / 2))
                ->  Hash Join
                      Hash Cond: (t2_3.b = t1_3.a)
                      ->  Seq Scan on prt2_p3 t2_3
@@ -926,7 +926,7 @@ SELECT t1.* FROM prt1 t1 WHERE t1.a IN (SELECT t1.b FROM prt2 t1, prt1_e t2 WHER
    Sort Key: t1.a
    ->  Append
          ->  Nested Loop
-               Join Filter: (t1_5.b = t1_2.a)
+               Join Filter: (t1_2.a = t1_5.b)
                ->  HashAggregate
                      Group Key: t1_5.b
                      ->  Hash Join
@@ -939,7 +939,7 @@ SELECT t1.* FROM prt1 t1 WHERE t1.a IN (SELECT t1.b FROM prt2 t1, prt1_e t2 WHER
                      Index Cond: (a = ((t2_1.a + t2_1.b) / 2))
                      Filter: (b = 0)
          ->  Nested Loop
-               Join Filter: (t1_6.b = t1_3.a)
+               Join Filter: (t1_3.a = t1_6.b)
                ->  HashAggregate
                      Group Key: t1_6.b
                      ->  Hash Join
@@ -952,7 +952,7 @@ SELECT t1.* FROM prt1 t1 WHERE t1.a IN (SELECT t1.b FROM prt2 t1, prt1_e t2 WHER
                      Index Cond: (a = ((t2_2.a + t2_2.b) / 2))
                      Filter: (b = 0)
          ->  Nested Loop
-               Join Filter: (t1_7.b = t1_4.a)
+               Join Filter: (t1_4.a = t1_7.b)
                ->  HashAggregate
                      Group Key: t1_7.b
                      ->  Nested Loop
commit 376b24da1de84c7a445af9282de569fb2fbceb1b
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:38:40 2023 -0500

    Fix flatten_join_alias_vars() to handle varnullingrels correctly.
    
    The remaining core regression test failures occur because
    flatten_join_alias_vars() isn't doing the right thing.  The
    alias Var it needs to replace may have acquired varnullingrels
    bits signifying the effect of upper outer joins, and if so we
    must preserve that information in the replacement expression.
    
    The simplest way to do that is to wrap the replacement expression
    in a PlaceHolderVar, and that's what we have to do in the general
    case where subquery pullup has mutated the replacement joinaliasvars
    entry into an arbitrary expression.  But in simpler cases, such as
    where the joinaliasvars entry is just a Var, we'd prefer to do it
    by merging the alias Var's varnullingrels into the replacement Var.
    In that way the flattened alias will compare equal() to semantically
    equivalent references that didn't use the alias name.
    
    Moreover, the parser also uses this code while checking certain
    semantic constraints, and in that context we *must not* generate
    PlaceHolderVars.  PHVs shouldn't appear in parse-time expressions,
    and adding one would certainly cause the parser to decide the
    query is invalid (because the result wouldn't compare equal() to
    what it needs to).  Fortunately, during parsing the set of possible
    contents of a joinaliasvars entry is quite constrained, so we can
    guarantee to apply the nullingrels info to the Vars therein.
    
    The result of this step passes all core regression tests, but there
    are still loose ends for FDWs (so that contrib/postgres_fdw will fail).

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 12fe442980..320caebd87 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -913,7 +913,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 			 */
 			if (rte->lateral && root->hasJoinRTEs)
 				rte->subquery = (Query *)
-					flatten_join_alias_vars(root->parse,
+					flatten_join_alias_vars(root, root->parse,
 											(Node *) rte->subquery);
 		}
 		else if (rte->rtekind == RTE_FUNCTION)
@@ -1111,7 +1111,7 @@ preprocess_expression(PlannerInfo *root, Node *expr, int kind)
 		  kind == EXPRKIND_VALUES ||
 		  kind == EXPRKIND_TABLESAMPLE ||
 		  kind == EXPRKIND_TABLEFUNC))
-		expr = flatten_join_alias_vars(root->parse, expr);
+		expr = flatten_join_alias_vars(root, root->parse, expr);
 
 	/*
 	 * Simplify constant expressions.  For function RTEs, this was already
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index a5380361bf..9c96a558fc 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -1082,7 +1082,8 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	 * maybe even in the rewriter; but for now let's just fix this case here.)
 	 */
 	subquery->targetList = (List *)
-		flatten_join_alias_vars(subroot->parse, (Node *) subquery->targetList);
+		flatten_join_alias_vars(subroot, subroot->parse,
+								(Node *) subquery->targetList);
 
 	/*
 	 * Adjust level-0 varnos in subquery so that we can append its rangetable
diff --git a/src/backend/optimizer/util/var.c b/src/backend/optimizer/util/var.c
index b65de54cf8..509f307658 100644
--- a/src/backend/optimizer/util/var.c
+++ b/src/backend/optimizer/util/var.c
@@ -62,6 +62,7 @@ typedef struct
 
 typedef struct
 {
+	PlannerInfo *root;			/* could be NULL! */
 	Query	   *query;			/* outer Query */
 	int			sublevels_up;
 	bool		possible_sublink;	/* could aliases include a SubLink? */
@@ -80,6 +81,10 @@ static bool pull_var_clause_walker(Node *node,
 								   pull_var_clause_context *context);
 static Node *flatten_join_alias_vars_mutator(Node *node,
 											 flatten_join_alias_vars_context *context);
+static Node *add_nullingrels_if_needed(PlannerInfo *root, Node *newnode,
+									   Var *oldvar);
+static bool is_standard_join_alias_expression(Node *newnode, Var *oldvar);
+static void adjust_standard_join_alias_expression(Node *newnode, Var *oldvar);
 static Relids alias_relid_set(Query *query, Relids relids);

@@ -722,26 +727,42 @@ pull_var_clause_walker(Node *node, pull_var_clause_context *context)
  *	  is the only way that the executor can directly handle whole-row Vars.
  *
  * This also adjusts relid sets found in some expression node types to
- * substitute the contained base rels for any join relid.
+ * substitute the contained base+OJ rels for any join relid.
  *
  * If a JOIN contains sub-selects that have been flattened, its join alias
  * entries might now be arbitrary expressions, not just Vars.  This affects
- * this function in one important way: we might find ourselves inserting
- * SubLink expressions into subqueries, and we must make sure that their
- * Query.hasSubLinks fields get set to true if so.  If there are any
+ * this function in two important ways.  First, we might find ourselves
+ * inserting SubLink expressions into subqueries, and we must make sure that
+ * their Query.hasSubLinks fields get set to true if so.  If there are any
  * SubLinks in the join alias lists, the outer Query should already have
  * hasSubLinks = true, so this is only relevant to un-flattened subqueries.
+ * Second, we have to preserve any varnullingrels info attached to the
+ * alias Vars we're replacing.  If the replacement expression is a Var or
+ * PlaceHolderVar or constructed from those, we can just add the
+ * varnullingrels bits to the existing nullingrels field(s); otherwise
+ * we have to add a PlaceHolderVar wrapper.
  *
- * NOTE: this is used on not-yet-planned expressions.  We do not expect it
- * to be applied directly to the whole Query, so if we see a Query to start
- * with, we do want to increment sublevels_up (this occurs for LATERAL
- * subqueries).
+ * NOTE: this is also used by the parser, to expand join alias Vars before
+ * checking GROUP BY validity.  For that use-case, root will be NULL, which
+ * is why we have to pass the Query separately.  We need the root itself only
+ * for making PlaceHolderVars.  We can avoid making PlaceHolderVars in the
+ * parser's usage because it won't be dealing with arbitrary expressions:
+ * so long as adjust_standard_join_alias_expression can handle everything
+ * the parser would make as a join alias expression, we're OK.
  */
 Node *
-flatten_join_alias_vars(Query *query, Node *node)
+flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node)
 {
 	flatten_join_alias_vars_context context;
 
+	/*
+	 * We do not expect this to be applied to the whole Query, only to
+	 * expressions or LATERAL subqueries.  Hence, if the top node is a Query,
+	 * it's okay to immediately increment sublevels_up.
+	 */
+	Assert(node != (Node *) query);
+
+	context.root = root;
 	context.query = query;
 	context.sublevels_up = 0;
 	/* flag whether join aliases could possibly contain SubLinks */
@@ -812,7 +833,9 @@ flatten_join_alias_vars_mutator(Node *node,
 			rowexpr->colnames = colnames;
 			rowexpr->location = var->location;
 
-			return (Node *) rowexpr;
+			/* Lastly, add any varnullingrels to the replacement expression */
+			return add_nullingrels_if_needed(context->root, (Node *) rowexpr,
+											 var);
 		}
 
 		/* Expand join alias reference */
@@ -839,7 +862,8 @@ flatten_join_alias_vars_mutator(Node *node,
 		if (context->possible_sublink && !context->inserted_sublink)
 			context->inserted_sublink = checkExprHasSubLink(newvar);
 
-		return newvar;
+		/* Lastly, add any varnullingrels to the replacement expression */
+		return add_nullingrels_if_needed(context->root, newvar, var);
 	}
 	if (IsA(node, PlaceHolderVar))
 	{
@@ -854,6 +878,7 @@ flatten_join_alias_vars_mutator(Node *node,
 		{
 			phv->phrels = alias_relid_set(context->query,
 										  phv->phrels);
+			/* we *don't* change phnullingrels */
 		}
 		return (Node *) phv;
 	}
@@ -887,9 +912,145 @@ flatten_join_alias_vars_mutator(Node *node,
 								   (void *) context);
 }
 
+/*
+ * Add oldvar's varnullingrels, if any, to a flattened join alias expression.
+ * The newnode has been copied, so we can modify it freely.
+ */
+static Node *
+add_nullingrels_if_needed(PlannerInfo *root, Node *newnode, Var *oldvar)
+{
+	if (oldvar->varnullingrels == NULL)
+		return newnode;			/* nothing to do */
+	/* If possible, do it by adding to existing nullingrel fields */
+	if (is_standard_join_alias_expression(newnode, oldvar))
+		adjust_standard_join_alias_expression(newnode, oldvar);
+	else if (root)
+	{
+		/* We can insert a PlaceHolderVar to carry the nullingrels */
+		PlaceHolderVar *newphv;
+		Relids		phrels = pull_varnos(root, newnode);
+
+		/* XXX what if phrels is empty? */
+		Assert(!bms_is_empty(phrels));	/* probably wrong */
+		newphv = make_placeholder_expr(root, (Expr *) newnode, phrels);
+		/* newphv has zero phlevelsup and NULL phnullingrels; fix it */
+		newphv->phlevelsup = oldvar->varlevelsup;
+		newphv->phnullingrels = bms_copy(oldvar->varnullingrels);
+		newnode = (Node *) newphv;
+	}
+	else
+	{
+		/* ooops, we're missing support for something the parser can make */
+		elog(ERROR, "unsupported join alias expression");
+	}
+	return newnode;
+}
+
+/*
+ * Check to see if we can insert nullingrels into this join alias expression
+ * without use of a separate PlaceHolderVar.
+ *
+ * This will handle Vars, PlaceHolderVars, and implicit-coercion and COALESCE
+ * expressions built from those.  This coverage needs to handle anything
+ * that the parser would put into joinaliasvars.
+ * XXX it's probably incomplete at the moment.
+ */
+static bool
+is_standard_join_alias_expression(Node *newnode, Var *oldvar)
+{
+	if (newnode == NULL)
+		return false;
+	if (IsA(newnode, Var) &&
+		((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
+		return true;
+	else if (IsA(newnode, PlaceHolderVar) &&
+			 ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
+		return true;
+	else if (IsA(newnode, FuncExpr))
+	{
+		FuncExpr   *fexpr = (FuncExpr *) newnode;
+
+		/*
+		 * We need to assume that the function wouldn't produce non-NULL from
+		 * NULL, which is reasonable for implicit coercions but otherwise not
+		 * so much.  (Looking at its strictness is likely overkill, and anyway
+		 * it would cause us to fail if someone forgot to mark an implicit
+		 * coercion as strict.)
+		 */
+		if (fexpr->funcformat != COERCE_IMPLICIT_CAST ||
+			fexpr->args == NIL)
+			return false;
+
+		/*
+		 * Examine only the first argument --- coercions might have additional
+		 * arguments that are constants.
+		 */
+		return is_standard_join_alias_expression(linitial(fexpr->args), oldvar);
+	}
+	else if (IsA(newnode, CoalesceExpr))
+	{
+		CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
+		ListCell   *lc;
+
+		Assert(cexpr->args != NIL);
+		foreach(lc, cexpr->args)
+		{
+			if (!is_standard_join_alias_expression(lfirst(lc), oldvar))
+				return false;
+		}
+		return true;
+	}
+	else
+		return false;
+}
+
+/*
+ * Insert nullingrels into an expression accepted by
+ * is_standard_join_alias_expression.
+ */
+static void
+adjust_standard_join_alias_expression(Node *newnode, Var *oldvar)
+{
+	if (IsA(newnode, Var) &&
+		((Var *) newnode)->varlevelsup == oldvar->varlevelsup)
+	{
+		Var		   *newvar = (Var *) newnode;
+
+		newvar->varnullingrels = bms_add_members(newvar->varnullingrels,
+												 oldvar->varnullingrels);
+	}
+	else if (IsA(newnode, PlaceHolderVar) &&
+			 ((PlaceHolderVar *) newnode)->phlevelsup == oldvar->varlevelsup)
+	{
+		PlaceHolderVar *newphv = (PlaceHolderVar *) newnode;
+
+		newphv->phnullingrels = bms_add_members(newphv->phnullingrels,
+												oldvar->varnullingrels);
+	}
+	else if (IsA(newnode, FuncExpr))
+	{
+		FuncExpr   *fexpr = (FuncExpr *) newnode;
+
+		adjust_standard_join_alias_expression(linitial(fexpr->args), oldvar);
+	}
+	else if (IsA(newnode, CoalesceExpr))
+	{
+		CoalesceExpr *cexpr = (CoalesceExpr *) newnode;
+		ListCell   *lc;
+
+		Assert(cexpr->args != NIL);
+		foreach(lc, cexpr->args)
+		{
+			adjust_standard_join_alias_expression(lfirst(lc), oldvar);
+		}
+	}
+	else
+		Assert(false);
+}
+
 /*
  * alias_relid_set: in a set of RT indexes, replace joins by their
- * underlying base relids
+ * underlying base+OJ relids
  */
 static Relids
 alias_relid_set(Query *query, Relids relids)
diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index caecaaae50..4fbf80c271 100644
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -1167,7 +1167,7 @@ parseCheckAggregates(ParseState *pstate, Query *qry)
 	 * entries are RTE_JOIN kind.
 	 */
 	if (hasJoinRTEs)
-		groupClauses = (List *) flatten_join_alias_vars(qry,
+		groupClauses = (List *) flatten_join_alias_vars(NULL, qry,
 														(Node *) groupClauses);
 
 	/*
@@ -1211,7 +1211,7 @@ parseCheckAggregates(ParseState *pstate, Query *qry)
 							groupClauses, hasJoinRTEs,
 							have_non_var_grouping);
 	if (hasJoinRTEs)
-		clause = flatten_join_alias_vars(qry, clause);
+		clause = flatten_join_alias_vars(NULL, qry, clause);
 	check_ungrouped_columns(clause, pstate, qry,
 							groupClauses, groupClauseCommonVars,
 							have_non_var_grouping,
@@ -1222,7 +1222,7 @@ parseCheckAggregates(ParseState *pstate, Query *qry)
 							groupClauses, hasJoinRTEs,
 							have_non_var_grouping);
 	if (hasJoinRTEs)
-		clause = flatten_join_alias_vars(qry, clause);
+		clause = flatten_join_alias_vars(NULL, qry, clause);
 	check_ungrouped_columns(clause, pstate, qry,
 							groupClauses, groupClauseCommonVars,
 							have_non_var_grouping,
@@ -1551,7 +1551,7 @@ finalize_grouping_exprs_walker(Node *node,
 				Index		ref = 0;
 
 				if (context->hasJoinRTEs)
-					expr = flatten_join_alias_vars(context->qry, expr);
+					expr = flatten_join_alias_vars(NULL, context->qry, expr);
 
 				/*
 				 * Each expression must match a grouping entry at the current
diff --git a/src/include/optimizer/optimizer.h b/src/include/optimizer/optimizer.h
index 69ce6ee4d3..b6df013c21 100644
--- a/src/include/optimizer/optimizer.h
+++ b/src/include/optimizer/optimizer.h
@@ -197,6 +197,6 @@ extern bool contain_var_clause(Node *node);
 extern bool contain_vars_of_level(Node *node, int levelsup);
 extern int	locate_var_of_level(Node *node, int levelsup);
 extern List *pull_var_clause(Node *node, int flags);
-extern Node *flatten_join_alias_vars(Query *query, Node *node);
+extern Node *flatten_join_alias_vars(PlannerInfo *root, Query *query, Node *node);
 
 #endif							/* OPTIMIZER_H */
commit 82ea2fee2d71cd9f32fd9bc591d64780f2d7d6f4
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:45:35 2023 -0500

    Teach FDWs about base-plus-outer-join relids.
    
    Conversion of the planner to include OJ relids in join relids
    affects FDWs that want to plan foreign joins.  They *must* follow
    suit when labeling foreign joins in order to match with the core
    planner, but for many purposes (if postgres_fdw is any guide)
    they'd prefer to consider only base relations within the join.
    To support both requirements, redefine ForeignScan.fs_relids as
    base+OJ relids, and add a new field fs_base_relids that's set up
    by the core planner.
    
    Another way we could do this is to keep fs_relids as just base
    relids and make the new field be the one with OJ relids added.
    While that would be more backwards-compatible in some sense,
    it would be inconsistent with the naming used in the core planner,
    and I think that it might allow some types of bugs to escape
    quick detection.
    
    postgres_fdw also has one place where it needs to ignore varnullingrels
    while matching Vars.  It's not clear whether it's worth trying to
    improve that.  (This too is probably only an issue for FDWs that do
    join planning, since Vars seen in a base relation scan should never
    have any varnullingrels.)
    
    As of this step, this patch series again passes check-world.

diff --git a/contrib/postgres_fdw/deparse.c b/contrib/postgres_fdw/deparse.c
index 473fa45bd4..8a847deb13 100644
--- a/contrib/postgres_fdw/deparse.c
+++ b/contrib/postgres_fdw/deparse.c
@@ -4026,7 +4026,17 @@ get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
 	i = 1;
 	foreach(lc, foreignrel->reltarget->exprs)
 	{
-		if (equal(lfirst(lc), (Node *) node))
+		Var		   *tlvar = (Var *) lfirst(lc);
+
+		/*
+		 * Match reltarget entries only on varno/varattno.  Ideally there
+		 * would be some cross-check on varnullingrels, but it's unclear what
+		 * to do exactly; we don't have enough context to know what that value
+		 * should be.
+		 */
+		if (IsA(tlvar, Var) &&
+			tlvar->varno == node->varno &&
+			tlvar->varattno == node->varattno)
 		{
 			*colno = i;
 			return;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 50d23f922c..29b2be602c 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -1517,7 +1517,7 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 	if (fsplan->scan.scanrelid > 0)
 		rtindex = fsplan->scan.scanrelid;
 	else
-		rtindex = bms_next_member(fsplan->fs_relids, -1);
+		rtindex = bms_next_member(fsplan->fs_base_relids, -1);
 	rte = exec_rt_fetch(rtindex, estate);
 
 	/* Get info about foreign table. */
@@ -2414,7 +2414,7 @@ find_modifytable_subplan(PlannerInfo *root,
 	{
 		ForeignScan *fscan = (ForeignScan *) subplan;
 
-		if (bms_is_member(rtindex, fscan->fs_relids))
+		if (bms_is_member(rtindex, fscan->fs_base_relids))
 			return fscan;
 	}
 
@@ -2838,8 +2838,8 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
 		 * that setrefs.c won't update the string when flattening the
 		 * rangetable.  To find out what rtoffset was applied, identify the
 		 * minimum RT index appearing in the string and compare it to the
-		 * minimum member of plan->fs_relids.  (We expect all the relids in
-		 * the join will have been offset by the same amount; the Asserts
+		 * minimum member of plan->fs_base_relids.  (We expect all the relids
+		 * in the join will have been offset by the same amount; the Asserts
 		 * below should catch it if that ever changes.)
 		 */
 		minrti = INT_MAX;
@@ -2856,7 +2856,7 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
 			else
 				ptr++;
 		}
-		rtoffset = bms_next_member(plan->fs_relids, -1) - minrti;
+		rtoffset = bms_next_member(plan->fs_base_relids, -1) - minrti;
 
 		/* Now we can translate the string */
 		relations = makeStringInfo();
@@ -2871,7 +2871,7 @@ postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
 				char	   *refname;
 
 				rti += rtoffset;
-				Assert(bms_is_member(rti, plan->fs_relids));
+				Assert(bms_is_member(rti, plan->fs_base_relids));
 				rte = rt_fetch(rti, es->rtable);
 				Assert(rte->rtekind == RTE_RELATION);
 				/* This logic should agree with explain.c's ExplainTargetRel */
diff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgml
index 94263c628f..ac1717bc3c 100644
--- a/doc/src/sgml/fdwhandler.sgml
+++ b/doc/src/sgml/fdwhandler.sgml
@@ -351,6 +351,17 @@ GetForeignJoinPaths(PlannerInfo *root,
      it will supply at run time in the tuples it returns.
     </para>
 
+    <note>
+     <para>
+      Beginning with <productname>PostgreSQL</productname> 16,
+      <structfield>fs_relids</structfield> includes the rangetable indexes
+      of outer joins, if any were involved in this join.  The new field
+      <structfield>fs_base_relids</structfield> includes only base
+      relation indexes, and thus
+      mimics <structfield>fs_relids</structfield>'s old semantics.
+     </para>
+    </note>
+
     <para>
      See <xref linkend="fdw-planning"/> for additional information.
     </para>
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 5212a64b1e..1b0e1bc26a 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -1114,7 +1114,7 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
 			break;
 		case T_ForeignScan:
 			*rels_used = bms_add_members(*rels_used,
-										 ((ForeignScan *) plan)->fs_relids);
+										 ((ForeignScan *) plan)->fs_base_relids);
 			break;
 		case T_CustomScan:
 			*rels_used = bms_add_members(*rels_used,
diff --git a/src/backend/executor/execScan.c b/src/backend/executor/execScan.c
index abe8432853..cf1871b0f5 100644
--- a/src/backend/executor/execScan.c
+++ b/src/backend/executor/execScan.c
@@ -325,7 +325,7 @@ ExecScanReScan(ScanState *node)
 			 * all of them.
 			 */
 			if (IsA(node->ps.plan, ForeignScan))
-				relids = ((ForeignScan *) node->ps.plan)->fs_relids;
+				relids = ((ForeignScan *) node->ps.plan)->fs_base_relids;
 			else if (IsA(node->ps.plan, CustomScan))
 				relids = ((CustomScan *) node->ps.plan)->custom_relids;
 			else
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index cd68942af0..4c99b28d0a 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -4158,14 +4158,22 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
 
 	/*
 	 * Likewise, copy the relids that are represented by this foreign scan. An
-	 * upper rel doesn't have relids set, but it covers all the base relations
-	 * participating in the underlying scan, so use root's all_baserels.
+	 * upper rel doesn't have relids set, but it covers all the relations
+	 * participating in the underlying scan/join, so use root->all_query_rels.
 	 */
 	if (rel->reloptkind == RELOPT_UPPER_REL)
-		scan_plan->fs_relids = root->all_baserels;
+		scan_plan->fs_relids = root->all_query_rels;
 	else
 		scan_plan->fs_relids = best_path->path.parent->relids;
 
+	/*
+	 * Join relid sets include relevant outer joins, but FDWs may need to know
+	 * which are the included base rels.  That's a bit tedious to get without
+	 * access to the plan-time data structures, so compute it here.
+	 */
+	scan_plan->fs_base_relids = bms_difference(scan_plan->fs_relids,
+											   root->outer_join_rels);
+
 	/*
 	 * If this is a foreign join, and to make it valid to push down we had to
 	 * assume that the current user is the same as some user explicitly named
@@ -5806,8 +5814,9 @@ make_foreignscan(List *qptlist,
 	node->fdw_private = fdw_private;
 	node->fdw_scan_tlist = fdw_scan_tlist;
 	node->fdw_recheck_quals = fdw_recheck_quals;
-	/* fs_relids will be filled in by create_foreignscan_plan */
+	/* fs_relids, fs_base_relids will be filled by create_foreignscan_plan */
 	node->fs_relids = NULL;
+	node->fs_base_relids = NULL;
 	/* fsSystemCol will be filled in by create_foreignscan_plan */
 	node->fsSystemCol = false;
 
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 8ea257f492..fb28dead4d 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1633,6 +1633,7 @@ set_foreignscan_references(PlannerInfo *root,
 	}
 
 	fscan->fs_relids = offset_relid_set(fscan->fs_relids, rtoffset);
+	fscan->fs_base_relids = offset_relid_set(fscan->fs_base_relids, rtoffset);
 
 	/* Adjust resultRelation if it's valid */
 	if (fscan->resultRelation > 0)
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index c1234fcf36..4781a9c632 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -695,6 +695,7 @@ typedef struct WorkTableScan
  * When the plan node represents a foreign join, scan.scanrelid is zero and
  * fs_relids must be consulted to identify the join relation.  (fs_relids
  * is valid for simple scans as well, but will always match scan.scanrelid.)
+ * fs_relids includes outer joins; fs_base_relids does not.
  *
  * If the FDW's PlanDirectModify() callback decides to repurpose a ForeignScan
  * node to perform the UPDATE or DELETE operation directly in the remote
@@ -716,7 +717,8 @@ typedef struct ForeignScan
 	List	   *fdw_private;	/* private data for FDW */
 	List	   *fdw_scan_tlist; /* optional tlist describing scan tuple */
 	List	   *fdw_recheck_quals;	/* original quals not in scan.plan.qual */
-	Bitmapset  *fs_relids;		/* RTIs generated by this scan */
+	Bitmapset  *fs_relids;		/* base+OJ RTIs generated by this scan */
+	Bitmapset  *fs_base_relids; /* base RTIs generated by this scan */
 	bool		fsSystemCol;	/* true if any "system column" is needed */
 } ForeignScan;
 
commit f4b47feed8a8a2307121cfbecda7105930143f61
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:51:02 2023 -0500

    Don't use RestrictInfo.nullable_relids in join_clause_is_movable_to.
    
    Instead of using per-clause nullable_relids data, compute a
    per-baserel set of outer joins that can null each relation, and
    check for overlap between that and clause_relids to detect whether
    the clause can safely be pushed down to relation scan level.
    
    join_clause_is_movable_into also uses nullable_relids, but it
    turns out that that test can just be dropped entirely.  Now that
    clause_relids includes nulling outer joins, the preceding tests
    in the function are sufficient to reject clauses that can't be
    pushed down.
    
    This might seem like a net loss given that we have to add a bit
    of code to initsplan.c to compute RelOptInfo.nulling_relids.
    However, that's not much code at all, and the payoff is this:
    we no longer need RestrictInfo.nullable_relids at all.
    The next patch, which removes that field and the extensive
    infrastructure that maintains it, saves way more code and cycles
    than we add here.  Also, I think there are likely going to be
    other uses for RelOptInfo.nulling_relids.

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 7db8291549..c285806a81 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -94,6 +94,8 @@ static void deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 static void process_security_barrier_quals(PlannerInfo *root,
 										   int rti, Relids qualscope,
 										   bool below_outer_join);
+static void mark_rels_nulled_by_join(PlannerInfo *root, Index ojrelid,
+									 Relids lower_rels);
 static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
 										   Relids left_rels, Relids right_rels,
 										   Relids inner_join_rels,
@@ -976,6 +978,8 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 													   j->rtindex);
 					root->outer_join_rels = bms_add_member(root->outer_join_rels,
 														   j->rtindex);
+					mark_rels_nulled_by_join(root, j->rtindex,
+											 right_item->qualscope);
 				}
 				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
 													right_item->inner_join_rels);
@@ -1031,6 +1035,10 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 												   j->rtindex);
 				root->outer_join_rels = bms_add_member(root->outer_join_rels,
 													   j->rtindex);
+				mark_rels_nulled_by_join(root, j->rtindex,
+										 left_item->qualscope);
+				mark_rels_nulled_by_join(root, j->rtindex,
+										 right_item->qualscope);
 				jtitem->inner_join_rels = bms_union(left_item->inner_join_rels,
 													right_item->inner_join_rels);
 				jtitem->left_rels = left_item->qualscope;
@@ -1345,6 +1353,33 @@ process_security_barrier_quals(PlannerInfo *root,
 	Assert(security_level <= root->qual_security_level);
 }
 
+/*
+ * mark_rels_nulled_by_join
+ *	  Fill RelOptInfo.nulling_relids of baserels nulled by this outer join
+ *
+ * Inputs:
+ *	ojrelid: RT index of the join RTE (must not be 0)
+ *	lower_rels: the base+OJ Relids syntactically below nullable side of join
+ */
+static void
+mark_rels_nulled_by_join(PlannerInfo *root, Index ojrelid,
+						 Relids lower_rels)
+{
+	int			relid = -1;
+
+	while ((relid = bms_next_member(lower_rels, relid)) > 0)
+	{
+		RelOptInfo *rel = root->simple_rel_array[relid];
+
+		if (rel == NULL)		/* must be an outer join */
+		{
+			Assert(bms_is_member(relid, root->outer_join_rels));
+			continue;
+		}
+		rel->nulling_relids = bms_add_member(rel->nulling_relids, ojrelid);
+	}
+}
+
 /*
  * make_outerjoininfo
  *	  Build a SpecialJoinInfo for the current outer join
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index ebfb4ddd12..6e0e3a1a58 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -283,6 +283,12 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 		rel->top_parent = parent->top_parent ? parent->top_parent : parent;
 		rel->top_parent_relids = rel->top_parent->relids;
 
+		/*
+		 * A child rel is below the same outer joins as its parent.  (We
+		 * presume this info was already calculated for the parent.)
+		 */
+		rel->nulling_relids = parent->nulling_relids;
+
 		/*
 		 * Also propagate lateral-reference information from appendrel parent
 		 * rels to their child rels.  We intentionally give each child rel the
@@ -306,6 +312,7 @@ build_simple_rel(PlannerInfo *root, int relid, RelOptInfo *parent)
 		rel->parent = NULL;
 		rel->top_parent = NULL;
 		rel->top_parent_relids = NULL;
+		rel->nulling_relids = NULL;
 		rel->direct_lateral_relids = NULL;
 		rel->lateral_relids = NULL;
 		rel->lateral_referencers = NULL;
@@ -685,6 +692,7 @@ build_join_rel(PlannerInfo *root,
 	joinrel->max_attr = 0;
 	joinrel->attr_needed = NULL;
 	joinrel->attr_widths = NULL;
+	joinrel->nulling_relids = NULL;
 	joinrel->lateral_vars = NIL;
 	joinrel->lateral_referencers = NULL;
 	joinrel->indexlist = NIL;
@@ -874,6 +882,7 @@ build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 	joinrel->max_attr = 0;
 	joinrel->attr_needed = NULL;
 	joinrel->attr_widths = NULL;
+	joinrel->nulling_relids = NULL;
 	joinrel->lateral_vars = NIL;
 	joinrel->lateral_referencers = NULL;
 	joinrel->indexlist = NIL;
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index 1350f011a6..e3b43a7cf3 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -618,8 +618,17 @@ join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
 	if (bms_is_member(baserel->relid, rinfo->outer_relids))
 		return false;
 
-	/* Target rel must not be nullable below the clause */
-	if (bms_is_member(baserel->relid, rinfo->nullable_relids))
+	/*
+	 * Target rel's Vars must not be nulled by any outer join.  We can check
+	 * this without groveling through the individual Vars by seeing whether
+	 * clause_relids (which includes all such Vars' varnullingrels) includes
+	 * any outer join that can null the target rel.  You might object that
+	 * this could reject the clause on the basis of an OJ relid that came from
+	 * some other rel's Var.  However, that would still mean that the clause
+	 * came from above that outer join and shouldn't be pushed down; so there
+	 * should be no false positives.
+	 */
+	if (bms_overlap(rinfo->clause_relids, baserel->nulling_relids))
 		return false;
 
 	/* Clause must not use any rels with LATERAL references to this rel */
@@ -651,16 +660,17 @@ join_clause_is_movable_to(RestrictInfo *rinfo, RelOptInfo *baserel)
  * relation plus the outer rels.  We also check that it does reference at
  * least one current Var, ensuring that the clause will be pushed down to
  * a unique place in a parameterized join tree.  And we check that we're
- * not pushing the clause into its outer-join outer side, nor down into
- * a lower outer join's inner side.
- *
- * The check about pushing a clause down into a lower outer join's inner side
- * is only approximate; it sometimes returns "false" when actually it would
- * be safe to use the clause here because we're still above the outer join
- * in question.  This is okay as long as the answers at different join levels
- * are consistent: it just means we might sometimes fail to push a clause as
- * far down as it could safely be pushed.  It's unclear whether it would be
- * worthwhile to do this more precisely.  (But if it's ever fixed to be
+ * not pushing the clause into its outer-join outer side.
+ *
+ * We used to need to check that we're not pushing the clause into a lower
+ * outer join's inner side.  However, now that clause_relids includes
+ * references to potentially-nulling outer joins, the other tests handle that
+ * concern.  If the clause references any Var coming from the inside of a
+ * lower outer join, its clause_relids will mention that outer join, causing
+ * the evaluability check to fail; while if it references no such Vars, the
+ * references-a-target-rel check will fail.
+ *
+ * XXX not clear if we can do this yet: (But if it's ever fixed to be
  * exactly accurate, there's an Assert in get_joinrel_parampathinfo() that
  * should be re-enabled.)
  *
@@ -704,14 +714,5 @@ join_clause_is_movable_into(RestrictInfo *rinfo,
 	if (bms_overlap(currentrelids, rinfo->outer_relids))
 		return false;
 
-	/*
-	 * Target rel(s) must not be nullable below the clause.  This is
-	 * approximate, in the safe direction, because the current join might be
-	 * above the join where the nulling would happen, in which case the clause
-	 * would work correctly here.  But we don't have enough info to be sure.
-	 */
-	if (bms_overlap(currentrelids, rinfo->nullable_relids))
-		return false;
-
 	return true;
 }
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 630a044089..cbe99ca397 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -694,6 +694,7 @@ typedef struct PartitionSchemeData *PartitionScheme;
  *				the attribute is needed as part of final targetlist
  *		attr_widths - cache space for per-attribute width estimates;
  *					  zero means not computed yet
+ *		nulling_relids - relids of outer joins that can null this rel
  *		lateral_vars - lateral cross-references of rel, if any (list of
  *					   Vars and PlaceHolderVars)
  *		lateral_referencers - relids of rels that reference this one laterally
@@ -927,6 +928,8 @@ typedef struct RelOptInfo
 	Relids	   *attr_needed pg_node_attr(read_write_ignore);
 	/* array indexed [min_attr .. max_attr] */
 	int32	   *attr_widths pg_node_attr(read_write_ignore);
+	/* relids of outer joins that can null this baserel */
+	Relids		nulling_relids;
 	/* LATERAL Vars and PHVs referenced by rel */
 	List	   *lateral_vars;
 	/* rels that reference this baserel laterally */
commit dd1a14bb08b999f17407fbec447ef5e19ceff266
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 14:59:37 2023 -0500

    Remove RestrictInfo.nullable_relids and associated infrastructure.
    
    There is no more code using this field, only code computing it,
    so just delete all that.  We can likewise get rid of
    EquivalenceMember.em_nullable_relids and
    PlannerInfo.nullable_baserels.

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 29b2be602c..d95e70dfce 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -6525,7 +6525,6 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 									  false,
 									  root->qual_security_level,
 									  grouped_rel->relids,
-									  NULL,
 									  NULL);
 			if (is_foreign_expr(root, grouped_rel, expr))
 				fpinfo->remote_conds = lappend(fpinfo->remote_conds, rinfo);
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index 26b294d5d0..ae0f9bdc8a 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2745,7 +2745,6 @@ set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 		if (var)
 			pathkeys = build_expression_pathkey(root,
 												(Expr *) var,
-												NULL,	/* below outer joins */
 												Int8LessOperator,
 												rel->relids,
 												false);
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 6cbb72a672..6f81cc2b08 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -34,7 +34,7 @@

 static EquivalenceMember *add_eq_member(EquivalenceClass *ec,
-										Expr *expr, Relids relids, Relids nullable_relids,
+										Expr *expr, Relids relids,
 										EquivalenceMember *parent,
 										Oid datatype);
 static bool is_exprlist_member(Expr *node, List *exprs);
@@ -131,9 +131,7 @@ process_equivalence(PlannerInfo *root,
 	Expr	   *item1;
 	Expr	   *item2;
 	Relids		item1_relids,
-				item2_relids,
-				item1_nullable_relids,
-				item2_nullable_relids;
+				item2_relids;
 	List	   *opfamilies;
 	EquivalenceClass *ec1,
 			   *ec2;
@@ -206,8 +204,7 @@ process_equivalence(PlannerInfo *root,
 								  restrictinfo->pseudoconstant,
 								  restrictinfo->security_level,
 								  NULL,
-								  restrictinfo->outer_relids,
-								  restrictinfo->nullable_relids);
+								  restrictinfo->outer_relids);
 		}
 		return false;
 	}
@@ -225,12 +222,6 @@ process_equivalence(PlannerInfo *root,
 			return false;		/* RHS is non-strict but not constant */
 	}
 
-	/* Calculate nullable-relid sets for each side of the clause */
-	item1_nullable_relids = bms_intersect(item1_relids,
-										  restrictinfo->nullable_relids);
-	item2_nullable_relids = bms_intersect(item2_relids,
-										  restrictinfo->nullable_relids);
-
 	/*
 	 * We use the declared input types of the operator, not exprType() of the
 	 * inputs, as the nominal datatypes for opfamily lookup.  This presumes
@@ -400,7 +391,7 @@ process_equivalence(PlannerInfo *root,
 	else if (ec1)
 	{
 		/* Case 3: add item2 to ec1 */
-		em2 = add_eq_member(ec1, item2, item2_relids, item2_nullable_relids,
+		em2 = add_eq_member(ec1, item2, item2_relids,
 							NULL, item2_type);
 		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
 		ec1->ec_below_outer_join |= below_outer_join;
@@ -418,7 +409,7 @@ process_equivalence(PlannerInfo *root,
 	else if (ec2)
 	{
 		/* Case 3: add item1 to ec2 */
-		em1 = add_eq_member(ec2, item1, item1_relids, item1_nullable_relids,
+		em1 = add_eq_member(ec2, item1, item1_relids,
 							NULL, item1_type);
 		ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
 		ec2->ec_below_outer_join |= below_outer_join;
@@ -452,9 +443,9 @@ process_equivalence(PlannerInfo *root,
 		ec->ec_min_security = restrictinfo->security_level;
 		ec->ec_max_security = restrictinfo->security_level;
 		ec->ec_merged = NULL;
-		em1 = add_eq_member(ec, item1, item1_relids, item1_nullable_relids,
+		em1 = add_eq_member(ec, item1, item1_relids,
 							NULL, item1_type);
-		em2 = add_eq_member(ec, item2, item2_relids, item2_nullable_relids,
+		em2 = add_eq_member(ec, item2, item2_relids,
 							NULL, item2_type);
 
 		root->eq_classes = lappend(root->eq_classes, ec);
@@ -545,13 +536,12 @@ canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
  */
 static EquivalenceMember *
 add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
-			  Relids nullable_relids, EquivalenceMember *parent, Oid datatype)
+			  EquivalenceMember *parent, Oid datatype)
 {
 	EquivalenceMember *em = makeNode(EquivalenceMember);
 
 	em->em_expr = expr;
 	em->em_relids = relids;
-	em->em_nullable_relids = nullable_relids;
 	em->em_is_const = false;
 	em->em_is_child = (parent != NULL);
 	em->em_datatype = datatype;
@@ -588,13 +578,6 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
  *	  equivalence class it is a member of; if none, optionally build a new
  *	  single-member EquivalenceClass for it.
  *
- * expr is the expression, and nullable_relids is the set of base relids
- * that are potentially nullable below it.  We actually only care about
- * the set of such relids that are used in the expression; but for caller
- * convenience, we perform that intersection step here.  The caller need
- * only be sure that nullable_relids doesn't omit any nullable rels that
- * might appear in the expr.
- *
  * sortref is the SortGroupRef of the originating SortGroupClause, if any,
  * or zero if not.  (It should never be zero if the expression is volatile!)
  *
@@ -623,7 +606,6 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
 EquivalenceClass *
 get_eclass_for_sort_expr(PlannerInfo *root,
 						 Expr *expr,
-						 Relids nullable_relids,
 						 List *opfamilies,
 						 Oid opcintype,
 						 Oid collation,
@@ -719,13 +701,12 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 		elog(ERROR, "volatile EquivalenceClass has no sortref");
 
 	/*
-	 * Get the precise set of nullable relids appearing in the expression.
+	 * Get the precise set of relids appearing in the expression.
 	 */
 	expr_relids = pull_varnos(root, (Node *) expr);
-	nullable_relids = bms_intersect(nullable_relids, expr_relids);
 
 	newem = add_eq_member(newec, copyObject(expr), expr_relids,
-						  nullable_relids, NULL, opcintype);
+						  NULL, opcintype);
 
 	/*
 	 * add_eq_member doesn't check for volatile functions, set-returning
@@ -1211,8 +1192,6 @@ generate_base_implied_equalities_const(PlannerInfo *root,
 		rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
 										 cur_em->em_expr, const_em->em_expr,
 										 bms_copy(ec->ec_relids),
-										 bms_union(cur_em->em_nullable_relids,
-												   const_em->em_nullable_relids),
 										 ec->ec_min_security,
 										 ec->ec_below_outer_join,
 										 cur_em->em_is_const);
@@ -1285,8 +1264,6 @@ generate_base_implied_equalities_no_const(PlannerInfo *root,
 			rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
 											 prev_em->em_expr, cur_em->em_expr,
 											 bms_copy(ec->ec_relids),
-											 bms_union(prev_em->em_nullable_relids,
-													   cur_em->em_nullable_relids),
 											 ec->ec_min_security,
 											 ec->ec_below_outer_join,
 											 false);
@@ -1889,8 +1866,6 @@ create_join_clause(PlannerInfo *root,
 										rightem->em_expr,
 										bms_union(leftem->em_relids,
 												  rightem->em_relids),
-										bms_union(leftem->em_nullable_relids,
-												  rightem->em_nullable_relids),
 										ec->ec_min_security);
 
 	/* If it's a child clause, copy the parent's rinfo_serial */
@@ -2110,8 +2085,7 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 				left_type,
 				right_type,
 				inner_datatype;
-	Relids		inner_relids,
-				inner_nullable_relids;
+	Relids		inner_relids;
 	ListCell   *lc1;
 
 	Assert(is_opclause(rinfo->clause));
@@ -2138,8 +2112,6 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 		inner_datatype = left_type;
 		inner_relids = rinfo->left_relids;
 	}
-	inner_nullable_relids = bms_intersect(inner_relids,
-										  rinfo->nullable_relids);
 
 	/* Scan EquivalenceClasses for a match to outervar */
 	foreach(lc1, root->eq_classes)
@@ -2200,7 +2172,6 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 												   innervar,
 												   cur_em->em_expr,
 												   bms_copy(inner_relids),
-												   bms_copy(inner_nullable_relids),
 												   cur_ec->ec_min_security);
 			if (process_equivalence(root, &newrinfo, true))
 				match = true;
@@ -2238,9 +2209,7 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 				left_type,
 				right_type;
 	Relids		left_relids,
-				right_relids,
-				left_nullable_relids,
-				right_nullable_relids;
+				right_relids;
 	ListCell   *lc1;
 
 	/* Can't use an outerjoin_delayed clause here */
@@ -2256,10 +2225,6 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 	rightvar = (Expr *) get_rightop(rinfo->clause);
 	left_relids = rinfo->left_relids;
 	right_relids = rinfo->right_relids;
-	left_nullable_relids = bms_intersect(left_relids,
-										 rinfo->nullable_relids);
-	right_nullable_relids = bms_intersect(right_relids,
-										  rinfo->nullable_relids);
 
 	foreach(lc1, root->eq_classes)
 	{
@@ -2361,7 +2326,6 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 													   leftvar,
 													   cur_em->em_expr,
 													   bms_copy(left_relids),
-													   bms_copy(left_nullable_relids),
 													   cur_ec->ec_min_security);
 				if (process_equivalence(root, &newrinfo, true))
 					matchleft = true;
@@ -2377,7 +2341,6 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 													   rightvar,
 													   cur_em->em_expr,
 													   bms_copy(right_relids),
-													   bms_copy(right_nullable_relids),
 													   cur_ec->ec_min_security);
 				if (process_equivalence(root, &newrinfo, true))
 					matchright = true;
@@ -2667,7 +2630,6 @@ add_child_rel_equivalences(PlannerInfo *root,
 				/* Yes, generate transformed child version */
 				Expr	   *child_expr;
 				Relids		new_relids;
-				Relids		new_nullable_relids;
 
 				if (parent_rel->reloptkind == RELOPT_BASEREL)
 				{
@@ -2697,21 +2659,7 @@ add_child_rel_equivalences(PlannerInfo *root,
 											top_parent_relids);
 				new_relids = bms_add_members(new_relids, child_relids);
 
-				/*
-				 * And likewise for nullable_relids.  Note this code assumes
-				 * parent and child relids are singletons.
-				 */
-				new_nullable_relids = cur_em->em_nullable_relids;
-				if (bms_overlap(new_nullable_relids, top_parent_relids))
-				{
-					new_nullable_relids = bms_difference(new_nullable_relids,
-														 top_parent_relids);
-					new_nullable_relids = bms_add_members(new_nullable_relids,
-														  child_relids);
-				}
-
-				(void) add_eq_member(cur_ec, child_expr,
-									 new_relids, new_nullable_relids,
+				(void) add_eq_member(cur_ec, child_expr, new_relids,
 									 cur_em, cur_em->em_datatype);
 
 				/* Record this EC index for the child rel */
@@ -2808,7 +2756,6 @@ add_child_join_rel_equivalences(PlannerInfo *root,
 				/* Yes, generate transformed child version */
 				Expr	   *child_expr;
 				Relids		new_relids;
-				Relids		new_nullable_relids;
 
 				if (parent_joinrel->reloptkind == RELOPT_JOINREL)
 				{
@@ -2839,20 +2786,7 @@ add_child_join_rel_equivalences(PlannerInfo *root,
 											top_parent_relids);
 				new_relids = bms_add_members(new_relids, child_relids);
 
-				/*
-				 * For nullable_relids, we must selectively replace parent
-				 * nullable relids with child ones.
-				 */
-				new_nullable_relids = cur_em->em_nullable_relids;
-				if (bms_overlap(new_nullable_relids, top_parent_relids))
-					new_nullable_relids =
-						adjust_child_relids_multilevel(root,
-													   new_nullable_relids,
-													   child_joinrel,
-													   child_joinrel->top_parent);
-
-				(void) add_eq_member(cur_ec, child_expr,
-									 new_relids, new_nullable_relids,
+				(void) add_eq_member(cur_ec, child_expr, new_relids,
 									 cur_em, cur_em->em_datatype);
 			}
 		}
diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index d2e241c983..c4e7f97f68 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -180,9 +180,6 @@ pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys)
  *	  Given an expression and sort-order information, create a PathKey.
  *	  The result is always a "canonical" PathKey, but it might be redundant.
  *
- * expr is the expression, and nullable_relids is the set of base relids
- * that are potentially nullable below it.
- *
  * If the PathKey is being generated from a SortGroupClause, sortref should be
  * the SortGroupClause's SortGroupRef; otherwise zero.
  *
@@ -198,7 +195,6 @@ pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys)
 static PathKey *
 make_pathkey_from_sortinfo(PlannerInfo *root,
 						   Expr *expr,
-						   Relids nullable_relids,
 						   Oid opfamily,
 						   Oid opcintype,
 						   Oid collation,
@@ -234,7 +230,7 @@ make_pathkey_from_sortinfo(PlannerInfo *root,
 			 equality_op);
 
 	/* Now find or (optionally) create a matching EquivalenceClass */
-	eclass = get_eclass_for_sort_expr(root, expr, nullable_relids,
+	eclass = get_eclass_for_sort_expr(root, expr,
 									  opfamilies, opcintype, collation,
 									  sortref, rel, create_it);
 
@@ -257,7 +253,6 @@ make_pathkey_from_sortinfo(PlannerInfo *root,
 static PathKey *
 make_pathkey_from_sortop(PlannerInfo *root,
 						 Expr *expr,
-						 Relids nullable_relids,
 						 Oid ordering_op,
 						 bool nulls_first,
 						 Index sortref,
@@ -279,7 +274,6 @@ make_pathkey_from_sortop(PlannerInfo *root,
 
 	return make_pathkey_from_sortinfo(root,
 									  expr,
-									  nullable_relids,
 									  opfamily,
 									  opcintype,
 									  collation,
@@ -584,12 +578,10 @@ build_index_pathkeys(PlannerInfo *root,
 		}
 
 		/*
-		 * OK, try to make a canonical pathkey for this sort key.  Note we're
-		 * underneath any outer joins, so nullable_relids should be NULL.
+		 * OK, try to make a canonical pathkey for this sort key.
 		 */
 		cpathkey = make_pathkey_from_sortinfo(root,
 											  indexkey,
-											  NULL,
 											  index->sortopfamily[i],
 											  index->opcintype[i],
 											  index->indexcollations[i],
@@ -743,14 +735,12 @@ build_partition_pathkeys(PlannerInfo *root, RelOptInfo *partrel,
 		/*
 		 * Try to make a canonical pathkey for this partkey.
 		 *
-		 * We're considering a baserel scan, so nullable_relids should be
-		 * NULL.  Also, we assume the PartitionDesc lists any NULL partition
-		 * last, so we treat the scan like a NULLS LAST index: we have
-		 * nulls_first for backwards scan only.
+		 * We assume the PartitionDesc lists any NULL partition last, so we
+		 * treat the scan like a NULLS LAST index: we have nulls_first for
+		 * backwards scan only.
 		 */
 		cpathkey = make_pathkey_from_sortinfo(root,
 											  keyCol,
-											  NULL,
 											  partscheme->partopfamily[i],
 											  partscheme->partopcintype[i],
 											  partscheme->partcollation[i],
@@ -799,7 +789,7 @@ build_partition_pathkeys(PlannerInfo *root, RelOptInfo *partrel,
  *	  Build a pathkeys list that describes an ordering by a single expression
  *	  using the given sort operator.
  *
- * expr, nullable_relids, and rel are as for make_pathkey_from_sortinfo.
+ * expr and rel are as for make_pathkey_from_sortinfo.
  * We induce the other arguments assuming default sort order for the operator.
  *
  * Similarly to make_pathkey_from_sortinfo, the result is NIL if create_it
@@ -808,7 +798,6 @@ build_partition_pathkeys(PlannerInfo *root, RelOptInfo *partrel,
 List *
 build_expression_pathkey(PlannerInfo *root,
 						 Expr *expr,
-						 Relids nullable_relids,
 						 Oid opno,
 						 Relids rel,
 						 bool create_it)
@@ -827,7 +816,6 @@ build_expression_pathkey(PlannerInfo *root,
 
 	cpathkey = make_pathkey_from_sortinfo(root,
 										  expr,
-										  nullable_relids,
 										  opfamily,
 										  opcintype,
 										  exprCollation((Node *) expr),
@@ -908,14 +896,11 @@ convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
 				 * expression is *not* volatile in the outer query: it's just
 				 * a Var referencing whatever the subquery emitted. (IOW, the
 				 * outer query isn't going to re-execute the volatile
-				 * expression itself.)	So this is okay.  Likewise, it's
-				 * correct to pass nullable_relids = NULL, because we're
-				 * underneath any outer joins appearing in the outer query.
+				 * expression itself.)	So this is okay.
 				 */
 				outer_ec =
 					get_eclass_for_sort_expr(root,
 											 (Expr *) outer_var,
-											 NULL,
 											 sub_eclass->ec_opfamilies,
 											 sub_member->em_datatype,
 											 sub_eclass->ec_collation,
@@ -997,7 +982,6 @@ convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
 					/* See if we have a matching EC for the TLE */
 					outer_ec = get_eclass_for_sort_expr(root,
 														(Expr *) outer_var,
-														NULL,
 														sub_eclass->ec_opfamilies,
 														sub_expr_type,
 														sub_expr_coll,
@@ -1138,13 +1122,6 @@ build_join_pathkeys(PlannerInfo *root,
  * The resulting PathKeys are always in canonical form.  (Actually, there
  * is no longer any code anywhere that creates non-canonical PathKeys.)
  *
- * We assume that root->nullable_baserels is the set of base relids that could
- * have gone to NULL below the SortGroupClause expressions.  This is okay if
- * the expressions came from the query's top level (ORDER BY, DISTINCT, etc)
- * and if this function is only invoked after deconstruct_jointree.  In the
- * future we might have to make callers pass in the appropriate
- * nullable-relids set, but for now it seems unnecessary.
- *
  * 'sortclauses' is a list of SortGroupClause nodes
  * 'tlist' is the targetlist to find the referenced tlist entries in
  */
@@ -1210,7 +1187,6 @@ make_pathkeys_for_sortclauses_extended(PlannerInfo *root,
 		}
 		pathkey = make_pathkey_from_sortop(root,
 										   sortkey,
-										   root->nullable_baserels,
 										   sortcl->sortop,
 										   sortcl->nulls_first,
 										   sortcl->tleSortGroupRef,
@@ -1268,7 +1244,6 @@ initialize_mergeclause_eclasses(PlannerInfo *root, RestrictInfo *restrictinfo)
 	restrictinfo->left_ec =
 		get_eclass_for_sort_expr(root,
 								 (Expr *) get_leftop(clause),
-								 restrictinfo->nullable_relids,
 								 restrictinfo->mergeopfamilies,
 								 lefttype,
 								 ((OpExpr *) clause)->inputcollid,
@@ -1278,7 +1253,6 @@ initialize_mergeclause_eclasses(PlannerInfo *root, RestrictInfo *restrictinfo)
 	restrictinfo->right_ec =
 		get_eclass_for_sort_expr(root,
 								 (Expr *) get_rightop(clause),
-								 restrictinfo->nullable_relids,
 								 restrictinfo->mergeopfamilies,
 								 righttype,
 								 ((OpExpr *) clause)->inputcollid,
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index c285806a81..934432b9c0 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -131,7 +131,7 @@ static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									List **postponed_qual_list,
 									List **postponed_oj_qual_list);
 static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
-								  Relids *nullable_relids_p, bool is_pushed_down);
+								  bool is_pushed_down);
 static bool check_equivalence_delay(PlannerInfo *root,
 									RestrictInfo *restrictinfo);
 static bool check_redundant_nullability_qual(PlannerInfo *root, Node *clause);
@@ -772,7 +772,6 @@ deconstruct_jointree(PlannerInfo *root)
 	/* These are filled as we scan the jointree */
 	root->all_baserels = NULL;
 	root->outer_join_rels = NULL;
-	root->nullable_baserels = NULL;
 
 	/* Perform the initial scan of the jointree */
 	result = deconstruct_recurse(root, (Node *) root->parse->jointree,
@@ -928,7 +927,6 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
-		Relids		nullable_rels;
 		JoinTreeItem *left_item,
 				   *right_item;
 		List	   *leftjoinlist,
@@ -954,8 +952,6 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->right_rels = right_item->qualscope;
 				/* Inner join adds no restrictions for quals */
 				jtitem->nonnullable_rels = NULL;
-				/* and it doesn't force anything to null, either */
-				nullable_rels = NULL;
 				break;
 			case JOIN_LEFT:
 			case JOIN_ANTI:
@@ -986,7 +982,6 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->left_rels = left_item->qualscope;
 				jtitem->right_rels = right_item->qualscope;
 				jtitem->nonnullable_rels = left_item->qualscope;
-				nullable_rels = right_item->qualscope;
 				break;
 			case JOIN_SEMI:
 				/* Recurse */
@@ -1009,13 +1004,6 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->right_rels = right_item->qualscope;
 				/* Semi join adds no restrictions for quals */
 				jtitem->nonnullable_rels = NULL;
-
-				/*
-				 * Theoretically, a semijoin would null the RHS; but since the
-				 * RHS can't be accessed above the join, this is immaterial
-				 * and we needn't account for it.
-				 */
-				nullable_rels = NULL;
 				break;
 			case JOIN_FULL:
 				/* Recurse */
@@ -1045,21 +1033,15 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->right_rels = right_item->qualscope;
 				/* each side is both outer and inner */
 				jtitem->nonnullable_rels = jtitem->qualscope;
-				nullable_rels = jtitem->qualscope;
 				break;
 			default:
 				/* JOIN_RIGHT was eliminated during reduce_outer_joins() */
 				elog(ERROR, "unrecognized join type: %d",
 					 (int) j->jointype);
 				leftjoinlist = rightjoinlist = NIL; /* keep compiler quiet */
-				nullable_rels = NULL;
 				break;
 		}
 
-		/* Report all rels that will be nulled anywhere in the jointree */
-		root->nullable_baserels = bms_add_members(root->nullable_baserels,
-												  nullable_rels);
-
 		/*
 		 * Compute the output joinlist.  We fold subproblems together except
 		 * at a FULL JOIN or where join_collapse_limit would be exceeded.
@@ -2210,7 +2192,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	bool		pseudoconstant = false;
 	bool		maybe_equivalence;
 	bool		maybe_outer_join;
-	Relids		nullable_relids;
 	RestrictInfo *restrictinfo;
 
 	/*
@@ -2364,7 +2345,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		/* Check to see if must be delayed by lower outer join */
 		outerjoin_delayed = check_outerjoin_delay(root,
 												  &relids,
-												  &nullable_relids,
 												  false);
 
 		/*
@@ -2392,7 +2372,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		/* Check to see if must be delayed by lower outer join */
 		outerjoin_delayed = check_outerjoin_delay(root,
 												  &relids,
-												  &nullable_relids,
 												  true);
 
 		if (outerjoin_delayed)
@@ -2452,8 +2431,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									 pseudoconstant,
 									 security_level,
 									 relids,
-									 outerjoin_nonnullable,
-									 nullable_relids);
+									 outerjoin_nonnullable);
 
 	/* Apply appropriate clone marking, too */
 	restrictinfo->has_clone = has_clone;
@@ -2611,9 +2589,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
  * If the qual must be delayed, add relids to *relids_p to reflect the lowest
  * safe level for evaluating the qual, and return true.  Any extra delay for
  * higher-level joins is reflected by setting delay_upper_joins to true in
- * SpecialJoinInfo structs.  We also compute nullable_relids, the set of
- * referenced relids that are nullable by lower outer joins (note that this
- * can be nonempty even for a non-delayed qual).
+ * SpecialJoinInfo structs.
  *
  * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
  * all the rels it mentions, and (2) we are at or above any outer joins that
@@ -2636,8 +2612,8 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
  * mentioning only C cannot be applied below the join to A.
  *
  * For a non-pushed-down qual, this isn't going to determine where we place the
- * qual, but we need to determine outerjoin_delayed and nullable_relids anyway
- * for use later in the planning process.
+ * qual, but we need to determine outerjoin_delayed anyway for use later in
+ * the planning process.
  *
  * Lastly, a pushed-down qual that references the nullable side of any current
  * join_info_list member and has to be evaluated above that OJ (because its
@@ -2655,24 +2631,18 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 static bool
 check_outerjoin_delay(PlannerInfo *root,
 					  Relids *relids_p, /* in/out parameter */
-					  Relids *nullable_relids_p,	/* output parameter */
 					  bool is_pushed_down)
 {
 	Relids		relids;
-	Relids		nullable_relids;
 	bool		outerjoin_delayed;
 	bool		found_some;
 
 	/* fast path if no special joins */
 	if (root->join_info_list == NIL)
-	{
-		*nullable_relids_p = NULL;
 		return false;
-	}
 
 	/* must copy relids because we need the original value at the end */
 	relids = bms_copy(*relids_p);
-	nullable_relids = NULL;
 	outerjoin_delayed = false;
 	do
 	{
@@ -2699,12 +2669,6 @@ check_outerjoin_delay(PlannerInfo *root,
 					/* we'll need another iteration */
 					found_some = true;
 				}
-				/* track all the nullable rels of relevant OJs */
-				nullable_relids = bms_add_members(nullable_relids,
-												  sjinfo->min_righthand);
-				if (sjinfo->jointype == JOIN_FULL)
-					nullable_relids = bms_add_members(nullable_relids,
-													  sjinfo->min_lefthand);
 				/* set delay_upper_joins if needed */
 				if (is_pushed_down && sjinfo->jointype != JOIN_FULL &&
 					bms_overlap(relids, sjinfo->min_lefthand))
@@ -2713,13 +2677,9 @@ check_outerjoin_delay(PlannerInfo *root,
 		}
 	} while (found_some);
 
-	/* identify just the actually-referenced nullable rels */
-	nullable_relids = bms_int_members(nullable_relids, *relids_p);
-
-	/* replace *relids_p, and return nullable_relids */
+	/* replace *relids_p */
 	bms_free(*relids_p);
 	*relids_p = relids;
-	*nullable_relids_p = nullable_relids;
 	return outerjoin_delayed;
 }
 
@@ -2741,7 +2701,6 @@ check_equivalence_delay(PlannerInfo *root,
 						RestrictInfo *restrictinfo)
 {
 	Relids		relids;
-	Relids		nullable_relids;
 
 	/* fast path if no special joins */
 	if (root->join_info_list == NIL)
@@ -2750,12 +2709,12 @@ check_equivalence_delay(PlannerInfo *root,
 	/* must copy restrictinfo's relids to avoid changing it */
 	relids = bms_copy(restrictinfo->left_relids);
 	/* check left side does not need delay */
-	if (check_outerjoin_delay(root, &relids, &nullable_relids, true))
+	if (check_outerjoin_delay(root, &relids, true))
 		return false;
 
 	/* and similarly for the right side */
 	relids = bms_copy(restrictinfo->right_relids);
-	if (check_outerjoin_delay(root, &relids, &nullable_relids, true))
+	if (check_outerjoin_delay(root, &relids, true))
 		return false;
 
 	return true;
@@ -2881,11 +2840,6 @@ distribute_restrictinfo_to_rels(PlannerInfo *root,
  * variable-free.  Otherwise the qual is applied at the lowest join level
  * that provides all its variables.
  *
- * "nullable_relids" is the set of relids used in the expressions that are
- * potentially nullable below the expressions.  (This has to be supplied by
- * caller because this function is used after deconstruct_jointree, so we
- * don't have knowledge of where the clause items came from.)
- *
  * "security_level" is the security level to assign to the new restrictinfo.
  *
  * "both_const" indicates whether both items are known pseudo-constant;
@@ -2911,7 +2865,6 @@ process_implied_equality(PlannerInfo *root,
 						 Expr *item1,
 						 Expr *item2,
 						 Relids qualscope,
-						 Relids nullable_relids,
 						 Index security_level,
 						 bool below_outer_join,
 						 bool both_const)
@@ -2995,8 +2948,7 @@ process_implied_equality(PlannerInfo *root,
 									 pseudoconstant,
 									 security_level,
 									 relids,
-									 NULL,	/* outer_relids */
-									 nullable_relids);
+									 NULL); /* outer_relids */
 
 	/*
 	 * If it's a join clause, add vars used in the clause to targetlists of
@@ -3061,7 +3013,6 @@ build_implied_join_equality(PlannerInfo *root,
 							Expr *item1,
 							Expr *item2,
 							Relids qualscope,
-							Relids nullable_relids,
 							Index security_level)
 {
 	RestrictInfo *restrictinfo;
@@ -3089,8 +3040,7 @@ build_implied_join_equality(PlannerInfo *root,
 									 false, /* pseudoconstant */
 									 security_level,	/* security_level */
 									 qualscope, /* required_relids */
-									 NULL,	/* outer_relids */
-									 nullable_relids);	/* nullable_relids */
+									 NULL); /* outer_relids */
 
 	/* Set mergejoinability/hashjoinability flags */
 	check_mergejoinable(restrictinfo);
diff --git a/src/backend/optimizer/util/appendinfo.c b/src/backend/optimizer/util/appendinfo.c
index dba895ccc4..d5869e0c1c 100644
--- a/src/backend/optimizer/util/appendinfo.c
+++ b/src/backend/optimizer/util/appendinfo.c
@@ -448,9 +448,6 @@ adjust_appendrel_attrs_mutator(Node *node,
 		newinfo->outer_relids = adjust_child_relids(oldinfo->outer_relids,
 													context->nappinfos,
 													context->appinfos);
-		newinfo->nullable_relids = adjust_child_relids(oldinfo->nullable_relids,
-													   context->nappinfos,
-													   context->appinfos);
 		newinfo->left_relids = adjust_child_relids(oldinfo->left_relids,
 												   context->nappinfos,
 												   context->appinfos);
diff --git a/src/backend/optimizer/util/inherit.c b/src/backend/optimizer/util/inherit.c
index bf3ea26cf4..7842baea49 100644
--- a/src/backend/optimizer/util/inherit.c
+++ b/src/backend/optimizer/util/inherit.c
@@ -897,7 +897,7 @@ apply_child_basequals(PlannerInfo *root, RelOptInfo *parentrel,
 												   rinfo->outerjoin_delayed,
 												   pseudoconstant,
 												   rinfo->security_level,
-												   NULL, NULL, NULL));
+												   NULL, NULL));
 			/* track minimum security level among child quals */
 			cq_min_security = Min(cq_min_security, rinfo->security_level);
 		}
@@ -932,7 +932,7 @@ apply_child_basequals(PlannerInfo *root, RelOptInfo *parentrel,
 									 make_restrictinfo(root, qual,
 													   true, false, false,
 													   security_level,
-													   NULL, NULL, NULL));
+													   NULL, NULL));
 				cq_min_security = Min(cq_min_security, security_level);
 			}
 			security_level++;
diff --git a/src/backend/optimizer/util/orclauses.c b/src/backend/optimizer/util/orclauses.c
index abc994dbf2..5c4a485d9f 100644
--- a/src/backend/optimizer/util/orclauses.c
+++ b/src/backend/optimizer/util/orclauses.c
@@ -275,7 +275,6 @@ consider_new_or_clause(PlannerInfo *root, RelOptInfo *rel,
 								 false,
 								 join_or_rinfo->security_level,
 								 NULL,
-								 NULL,
 								 NULL);
 
 	/*
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index e3b43a7cf3..87ad2d0ab5 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -29,8 +29,7 @@ static RestrictInfo *make_restrictinfo_internal(PlannerInfo *root,
 												bool pseudoconstant,
 												Index security_level,
 												Relids required_relids,
-												Relids outer_relids,
-												Relids nullable_relids);
+												Relids outer_relids);
 static Expr *make_sub_restrictinfos(PlannerInfo *root,
 									Expr *clause,
 									bool is_pushed_down,
@@ -38,8 +37,7 @@ static Expr *make_sub_restrictinfos(PlannerInfo *root,
 									bool pseudoconstant,
 									Index security_level,
 									Relids required_relids,
-									Relids outer_relids,
-									Relids nullable_relids);
+									Relids outer_relids);

 /*
@@ -49,7 +47,7 @@ static Expr *make_sub_restrictinfos(PlannerInfo *root,
  *
  * The is_pushed_down, outerjoin_delayed, and pseudoconstant flags for the
  * RestrictInfo must be supplied by the caller, as well as the correct values
- * for security_level, outer_relids, and nullable_relids.
+ * for security_level and outer_relids.
  * required_relids can be NULL, in which case it defaults to the actual clause
  * contents (i.e., clause_relids).
  *
@@ -69,8 +67,7 @@ make_restrictinfo(PlannerInfo *root,
 				  bool pseudoconstant,
 				  Index security_level,
 				  Relids required_relids,
-				  Relids outer_relids,
-				  Relids nullable_relids)
+				  Relids outer_relids)
 {
 	/*
 	 * If it's an OR clause, build a modified copy with RestrictInfos inserted
@@ -84,8 +81,7 @@ make_restrictinfo(PlannerInfo *root,
 													   pseudoconstant,
 													   security_level,
 													   required_relids,
-													   outer_relids,
-													   nullable_relids);
+													   outer_relids);
 
 	/* Shouldn't be an AND clause, else AND/OR flattening messed up */
 	Assert(!is_andclause(clause));
@@ -98,8 +94,7 @@ make_restrictinfo(PlannerInfo *root,
 									  pseudoconstant,
 									  security_level,
 									  required_relids,
-									  outer_relids,
-									  nullable_relids);
+									  outer_relids);
 }
 
 /*
@@ -116,8 +111,7 @@ make_restrictinfo_internal(PlannerInfo *root,
 						   bool pseudoconstant,
 						   Index security_level,
 						   Relids required_relids,
-						   Relids outer_relids,
-						   Relids nullable_relids)
+						   Relids outer_relids)
 {
 	RestrictInfo *restrictinfo = makeNode(RestrictInfo);
 	Relids		baserels;
@@ -132,7 +126,6 @@ make_restrictinfo_internal(PlannerInfo *root,
 	restrictinfo->can_join = false; /* may get set below */
 	restrictinfo->security_level = security_level;
 	restrictinfo->outer_relids = outer_relids;
-	restrictinfo->nullable_relids = nullable_relids;
 
 	/*
 	 * If it's potentially delayable by lower-level security quals, figure out
@@ -260,7 +253,7 @@ make_restrictinfo_internal(PlannerInfo *root,
  *
  * The same is_pushed_down, outerjoin_delayed, and pseudoconstant flag
  * values can be applied to all RestrictInfo nodes in the result.  Likewise
- * for security_level, outer_relids, and nullable_relids.
+ * for security_level and outer_relids.
  *
  * The given required_relids are attached to our top-level output,
  * but any OR-clause constituents are allowed to default to just the
@@ -274,8 +267,7 @@ make_sub_restrictinfos(PlannerInfo *root,
 					   bool pseudoconstant,
 					   Index security_level,
 					   Relids required_relids,
-					   Relids outer_relids,
-					   Relids nullable_relids)
+					   Relids outer_relids)
 {
 	if (is_orclause(clause))
 	{
@@ -291,8 +283,7 @@ make_sub_restrictinfos(PlannerInfo *root,
 													pseudoconstant,
 													security_level,
 													NULL,
-													outer_relids,
-													nullable_relids));
+													outer_relids));
 		return (Expr *) make_restrictinfo_internal(root,
 												   clause,
 												   make_orclause(orlist),
@@ -301,8 +292,7 @@ make_sub_restrictinfos(PlannerInfo *root,
 												   pseudoconstant,
 												   security_level,
 												   required_relids,
-												   outer_relids,
-												   nullable_relids);
+												   outer_relids);
 	}
 	else if (is_andclause(clause))
 	{
@@ -318,8 +308,7 @@ make_sub_restrictinfos(PlannerInfo *root,
 													 pseudoconstant,
 													 security_level,
 													 required_relids,
-													 outer_relids,
-													 nullable_relids));
+													 outer_relids));
 		return make_andclause(andlist);
 	}
 	else
@@ -331,8 +320,7 @@ make_sub_restrictinfos(PlannerInfo *root,
 												   pseudoconstant,
 												   security_level,
 												   required_relids,
-												   outer_relids,
-												   nullable_relids);
+												   outer_relids);
 }
 
 /*
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index cbe99ca397..522b2c08cc 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -268,14 +268,6 @@ struct PlannerInfo
 	 */
 	Relids		all_query_rels;
 
-	/*
-	 * nullable_baserels is a Relids set of base relids that are nullable by
-	 * some outer join in the jointree; these are rels that are potentially
-	 * nullable below the WHERE clause, SELECT targetlist, etc.  This is
-	 * computed in deconstruct_jointree.
-	 */
-	Relids		nullable_baserels;
-
 	/*
 	 * join_rel_list is a list of all join-relation RelOptInfos we have
 	 * considered in this planning run.  For small problems we just scan the
@@ -1392,7 +1384,6 @@ typedef struct EquivalenceMember
 
 	Expr	   *em_expr;		/* the expression represented */
 	Relids		em_relids;		/* all relids appearing in em_expr */
-	Relids		em_nullable_relids; /* nullable by lower outer joins */
 	bool		em_is_const;	/* expression is pseudoconstant? */
 	bool		em_is_child;	/* derived version for a child relation? */
 	Oid			em_datatype;	/* the "nominal type" used by the opfamily */
@@ -2418,9 +2409,7 @@ typedef struct LimitPath
  * in parameterized scans, since pushing it into the join's outer side would
  * lead to wrong answers.)
  *
- * There is also a nullable_relids field, which is the set of rels the clause
- * references that can be forced null by some outer join below the clause.
- *
+ * XXX this comment needs work, if we don't remove it completely:
  * outerjoin_delayed = true is subtly different from nullable_relids != NULL:
  * a clause might reference some nullable rels and yet not be
  * outerjoin_delayed because it also references all the other rels of the
@@ -2534,9 +2523,6 @@ typedef struct RestrictInfo
 	/* If an outer-join clause, the outer-side relations, else NULL: */
 	Relids		outer_relids;
 
-	/* The relids used in the clause that are nullable by lower outer joins: */
-	Relids		nullable_relids;
-
 	/*
 	 * Relids in the left/right side of the clause.  These fields are set for
 	 * any binary opclause.
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 9b38627efd..1b02a1dc08 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -128,7 +128,6 @@ extern Expr *canonicalize_ec_expression(Expr *expr,
 extern void reconsider_outer_join_clauses(PlannerInfo *root);
 extern EquivalenceClass *get_eclass_for_sort_expr(PlannerInfo *root,
 												  Expr *expr,
-												  Relids nullable_relids,
 												  List *opfamilies,
 												  Oid opcintype,
 												  Oid collation,
@@ -216,7 +215,7 @@ extern List *build_index_pathkeys(PlannerInfo *root, IndexOptInfo *index,
 extern List *build_partition_pathkeys(PlannerInfo *root, RelOptInfo *partrel,
 									  ScanDirection scandir, bool *partialkeys);
 extern List *build_expression_pathkey(PlannerInfo *root, Expr *expr,
-									  Relids nullable_relids, Oid opno,
+									  Oid opno,
 									  Relids rel, bool create_it);
 extern List *convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
 									   List *subquery_pathkeys,
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 95ecefdade..3e6e60f549 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -83,7 +83,6 @@ extern RestrictInfo *process_implied_equality(PlannerInfo *root,
 											  Expr *item1,
 											  Expr *item2,
 											  Relids qualscope,
-											  Relids nullable_relids,
 											  Index security_level,
 											  bool below_outer_join,
 											  bool both_const);
@@ -93,7 +92,6 @@ extern RestrictInfo *build_implied_join_equality(PlannerInfo *root,
 												 Expr *item1,
 												 Expr *item2,
 												 Relids qualscope,
-												 Relids nullable_relids,
 												 Index security_level);
 extern void match_foreign_keys_to_quals(PlannerInfo *root);
 
diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index c79bb420e4..f17c341c4b 100644
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -19,7 +19,7 @@
 
 /* Convenience macro for the common case of a valid-everywhere qual */
 #define make_simple_restrictinfo(root, clause)  \
-	make_restrictinfo(root, clause, true, false, false, 0, NULL, NULL, NULL)
+	make_restrictinfo(root, clause, true, false, false, 0, NULL, NULL)
 
 extern RestrictInfo *make_restrictinfo(PlannerInfo *root,
 									   Expr *clause,
@@ -28,8 +28,7 @@ extern RestrictInfo *make_restrictinfo(PlannerInfo *root,
 									   bool pseudoconstant,
 									   Index security_level,
 									   Relids required_relids,
-									   Relids outer_relids,
-									   Relids nullable_relids);
+									   Relids outer_relids);
 extern RestrictInfo *commute_restrictinfo(RestrictInfo *rinfo, Oid comm_op);
 extern bool restriction_is_or_clause(RestrictInfo *restrictinfo);
 extern bool restriction_is_securely_promotable(RestrictInfo *restrictinfo,
commit 50343c8060dc19b5dc7dc24bca5dcbefc31c0f9a
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 15:10:58 2023 -0500

    Use constant TRUE for "dummy" clauses when throwing back outer joins.
    
    This improves on a hack I introduced in commit 6a6522529.  If we
    have a left-join clause l.x = r.y, and a WHERE clause l.x = constant,
    we generate r.y = constant and then don't really have a need for the
    join clause.  Currently we throw the join clause back anyway after
    marking it redundant, so that the join search heuristics won't think
    this is a clauseless join and avoid it.  That was a kluge introduced
    under time pressure, and after looking at it I thought of a better
    way: let's just introduce constant-TRUE "join clauses" instead,
    and get rid of them at the end.
    
    This improves the generated plans for such cases by not having to
    test a redundant join clause.  We can also get rid of the ugly hack
    used to mark such clauses as redundant for selectivity estimation.
    
    The code added here should go away someday, if we can ever handle
    outer-join clauses as normal eclasses.  But the selectivity
    simplifications are good cleanup in any case.

diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 61db6ad951..435438a173 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -715,12 +715,6 @@ clause_selectivity_ext(PlannerInfo *root,
 				return (Selectivity) 1.0;
 		}
 
-		/*
-		 * If the clause is marked redundant, always return 1.0.
-		 */
-		if (rinfo->norm_selec > 1)
-			return (Selectivity) 1.0;
-
 		/*
 		 * If possible, cache the result of the selectivity calculation for
 		 * the clause.  We can cache if varRelid is zero or the clause
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 6f81cc2b08..f0eadbcfb9 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -1954,14 +1954,11 @@ create_join_clause(PlannerInfo *root,
  * If we don't find any match for a set-aside outer join clause, we must
  * throw it back into the regular joinclause processing by passing it to
  * distribute_restrictinfo_to_rels().  If we do generate a derived clause,
- * however, the outer-join clause is redundant.  We still throw it back,
- * because otherwise the join will be seen as a clauseless join and avoided
- * during join order searching; but we mark it as redundant to keep from
- * messing up the joinrel's size estimate.  (This behavior means that the
- * API for this routine is uselessly complex: we could have just put all
- * the clauses into the regular processing initially.  We keep it because
- * someday we might want to do something else, such as inserting "dummy"
- * joinclauses instead of real ones.)
+ * however, the outer-join clause is redundant.  We must still put some
+ * clause into the regular processing, because otherwise the join will be
+ * seen as a clauseless join and avoided during join order searching.
+ * We handle this by generating a constant-TRUE clause that is marked with
+ * required_relids that make it a join between the correct relations.
  *
  * Outer join clauses that are marked outerjoin_delayed are special: this
  * condition means that one or both VARs might go to null due to a lower
@@ -1996,10 +1993,15 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				/* remove it from the list */
 				root->left_join_clauses =
 					foreach_delete_current(root->left_join_clauses, cell);
-				/* we throw it back anyway (see notes above) */
-				/* but the thrown-back clause has no extra selectivity */
-				rinfo->norm_selec = 2.0;
-				rinfo->outer_selec = 1.0;
+				/* throw back a dummy replacement clause (see notes above) */
+				rinfo = make_restrictinfo(root,
+										  (Expr *) makeBoolConst(true, false),
+										  true, /* is_pushed_down */
+										  false,	/* outerjoin_delayed */
+										  false,	/* pseudoconstant */
+										  0,	/* security_level */
+										  rinfo->required_relids,
+										  rinfo->outer_relids);
 				distribute_restrictinfo_to_rels(root, rinfo);
 			}
 		}
@@ -2017,10 +2019,15 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				/* remove it from the list */
 				root->right_join_clauses =
 					foreach_delete_current(root->right_join_clauses, cell);
-				/* we throw it back anyway (see notes above) */
-				/* but the thrown-back clause has no extra selectivity */
-				rinfo->norm_selec = 2.0;
-				rinfo->outer_selec = 1.0;
+				/* throw back a dummy replacement clause (see notes above) */
+				rinfo = make_restrictinfo(root,
+										  (Expr *) makeBoolConst(true, false),
+										  true, /* is_pushed_down */
+										  false,	/* outerjoin_delayed */
+										  false,	/* pseudoconstant */
+										  0,	/* security_level */
+										  rinfo->required_relids,
+										  rinfo->outer_relids);
 				distribute_restrictinfo_to_rels(root, rinfo);
 			}
 		}
@@ -2038,10 +2045,15 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				/* remove it from the list */
 				root->full_join_clauses =
 					foreach_delete_current(root->full_join_clauses, cell);
-				/* we throw it back anyway (see notes above) */
-				/* but the thrown-back clause has no extra selectivity */
-				rinfo->norm_selec = 2.0;
-				rinfo->outer_selec = 1.0;
+				/* throw back a dummy replacement clause (see notes above) */
+				rinfo = make_restrictinfo(root,
+										  (Expr *) makeBoolConst(true, false),
+										  true, /* is_pushed_down */
+										  false,	/* outerjoin_delayed */
+										  false,	/* pseudoconstant */
+										  0,	/* security_level */
+										  rinfo->required_relids,
+										  rinfo->outer_relids);
 				distribute_restrictinfo_to_rels(root, rinfo);
 			}
 		}
diff --git a/src/backend/optimizer/util/orclauses.c b/src/backend/optimizer/util/orclauses.c
index 5c4a485d9f..e8972cd759 100644
--- a/src/backend/optimizer/util/orclauses.c
+++ b/src/backend/optimizer/util/orclauses.c
@@ -98,18 +98,13 @@ extract_restriction_or_clauses(PlannerInfo *root)
 		 * joinclause that is considered safe to move to this rel by the
 		 * parameterized-path machinery, even though what we are going to do
 		 * with it is not exactly a parameterized path.
-		 *
-		 * However, it seems best to ignore clauses that have been marked
-		 * redundant (by setting norm_selec > 1).  That likely can't happen
-		 * for OR clauses, but let's be safe.
 		 */
 		foreach(lc, rel->joininfo)
 		{
 			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
 
 			if (restriction_is_or_clause(rinfo) &&
-				join_clause_is_movable_to(rinfo, rel) &&
-				rinfo->norm_selec <= 1)
+				join_clause_is_movable_to(rinfo, rel))
 			{
 				/* Try to extract a qual for this rel only */
 				Expr	   *orclause = extract_or_clause(rinfo, rel);
@@ -355,7 +350,7 @@ consider_new_or_clause(PlannerInfo *root, RelOptInfo *rel,
 
 		/* And hack cached selectivity so join size remains the same */
 		join_or_rinfo->norm_selec = orig_selec / or_selec;
-		/* ensure result stays in sane range, in particular not "redundant" */
+		/* ensure result stays in sane range */
 		if (join_or_rinfo->norm_selec > 1)
 			join_or_rinfo->norm_selec = 1;
 		/* as explained above, we don't touch outer_selec */
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index 87ad2d0ab5..aafd74c7d2 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -424,6 +424,21 @@ restriction_is_securely_promotable(RestrictInfo *restrictinfo,
 		return false;
 }
 
+/*
+ * Detect whether a RestrictInfo's clause is constant TRUE (note that it's
+ * surely of type boolean).  No such WHERE clause could survive qual
+ * canonicalization, but equivclass.c may generate such RestrictInfos for
+ * reasons discussed therein.  We should drop them again when creating
+ * the finished plan, which is handled by the next few functions.
+ */
+static inline bool
+rinfo_is_constant_true(RestrictInfo *rinfo)
+{
+	return IsA(rinfo->clause, Const) &&
+		!((Const *) rinfo->clause)->constisnull &&
+		DatumGetBool(((Const *) rinfo->clause)->constvalue);
+}
+
 /*
  * get_actual_clauses
  *
@@ -443,6 +458,7 @@ get_actual_clauses(List *restrictinfo_list)
 		RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
 
 		Assert(!rinfo->pseudoconstant);
+		Assert(!rinfo_is_constant_true(rinfo));
 
 		result = lappend(result, rinfo->clause);
 	}
@@ -454,6 +470,7 @@ get_actual_clauses(List *restrictinfo_list)
  *
  * Extract bare clauses from 'restrictinfo_list', returning either the
  * regular ones or the pseudoconstant ones per 'pseudoconstant'.
+ * Constant-TRUE clauses are dropped in any case.
  */
 List *
 extract_actual_clauses(List *restrictinfo_list,
@@ -466,7 +483,8 @@ extract_actual_clauses(List *restrictinfo_list,
 	{
 		RestrictInfo *rinfo = lfirst_node(RestrictInfo, l);
 
-		if (rinfo->pseudoconstant == pseudoconstant)
+		if (rinfo->pseudoconstant == pseudoconstant &&
+			!rinfo_is_constant_true(rinfo))
 			result = lappend(result, rinfo->clause);
 	}
 	return result;
@@ -477,7 +495,7 @@ extract_actual_clauses(List *restrictinfo_list,
  *
  * Extract bare clauses from 'restrictinfo_list', separating those that
  * semantically match the join level from those that were pushed down.
- * Pseudoconstant clauses are excluded from the results.
+ * Pseudoconstant and constant-TRUE clauses are excluded from the results.
  *
  * This is only used at outer joins, since for plain joins we don't care
  * about pushed-down-ness.
@@ -499,13 +517,15 @@ extract_actual_join_clauses(List *restrictinfo_list,
 
 		if (RINFO_IS_PUSHED_DOWN(rinfo, joinrelids))
 		{
-			if (!rinfo->pseudoconstant)
+			if (!rinfo->pseudoconstant &&
+				!rinfo_is_constant_true(rinfo))
 				*otherquals = lappend(*otherquals, rinfo->clause);
 		}
 		else
 		{
 			/* joinquals shouldn't have been marked pseudoconstant */
 			Assert(!rinfo->pseudoconstant);
+			Assert(!rinfo_is_constant_true(rinfo));
 			*joinquals = lappend(*joinquals, rinfo->clause);
 		}
 	}
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 522b2c08cc..38a6f1adc8 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2568,10 +2568,7 @@ typedef struct RestrictInfo
 	/* eval cost of clause; -1 if not yet set */
 	QualCost	eval_cost pg_node_attr(equal_ignore);
 
-	/*
-	 * selectivity for "normal" (JOIN_INNER) semantics; -1 if not yet set; >1
-	 * means a redundant clause
-	 */
+	/* selectivity for "normal" (JOIN_INNER) semantics; -1 if not yet set */
 	Selectivity norm_selec pg_node_attr(equal_ignore);
 	/* selectivity for outer join semantics; -1 if not yet set */
 	Selectivity outer_selec pg_node_attr(equal_ignore);
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 360d87e1ed..6338d080d9 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -4064,8 +4064,8 @@ explain (costs off)
 select a.unique1, b.unique1, c.unique1, coalesce(b.twothousand, a.twothousand)
   from tenk1 a left join tenk1 b on b.thousand = a.unique1                        left join tenk1 c on c.unique2 = coalesce(b.twothousand, a.twothousand)
   where a.unique2 < 10 and coalesce(b.twothousand, a.twothousand) = 44;
-                                         QUERY PLAN                                          
----------------------------------------------------------------------------------------------
+                          QUERY PLAN                           
+---------------------------------------------------------------
  Nested Loop Left Join
    ->  Nested Loop Left Join
          Filter: (COALESCE(b.twothousand, a.twothousand) = 44)
@@ -4076,7 +4076,7 @@ select a.unique1, b.unique1, c.unique1, coalesce(b.twothousand, a.twothousand)
                ->  Bitmap Index Scan on tenk1_thous_tenthous
                      Index Cond: (thousand = a.unique1)
    ->  Index Scan using tenk1_unique2 on tenk1 c
-         Index Cond: ((unique2 = COALESCE(b.twothousand, a.twothousand)) AND (unique2 = 44))
+         Index Cond: (unique2 = 44)
 (11 rows)
 
 select a.unique1, b.unique1, c.unique1, coalesce(b.twothousand, a.twothousand)
@@ -4507,7 +4507,6 @@ where tt1.f1 = ss1.c0;
                Output: tt4.f1
                ->  Nested Loop Left Join
                      Output: tt4.f1
-                     Join Filter: (tt3.f1 = tt4.f1)
                      ->  Seq Scan on public.text_tbl tt3
                            Output: tt3.f1
                            Filter: (tt3.f1 = 'foo'::text)
@@ -4525,7 +4524,7 @@ where tt1.f1 = ss1.c0;
                      Output: (tt4.f1)
                      ->  Seq Scan on public.text_tbl tt5
                            Output: tt4.f1
-(33 rows)
+(32 rows)
 
 select 1 from
   text_tbl as tt1
@@ -4632,24 +4631,22 @@ explain (costs off)
                    QUERY PLAN                    
 -------------------------------------------------
  Nested Loop Left Join
-   Join Filter: (a.f1 = b.unique2)
    ->  Seq Scan on int4_tbl a
          Filter: (f1 = 0)
    ->  Index Scan using tenk1_unique2 on tenk1 b
          Index Cond: (unique2 = 0)
-(6 rows)
+(5 rows)
 
 explain (costs off)
   select * from tenk1 a full join tenk1 b using(unique2) where unique2 = 42;
                    QUERY PLAN                    
 -------------------------------------------------
  Merge Full Join
-   Merge Cond: (a.unique2 = b.unique2)
    ->  Index Scan using tenk1_unique2 on tenk1 a
          Index Cond: (unique2 = 42)
    ->  Index Scan using tenk1_unique2 on tenk1 b
          Index Cond: (unique2 = 42)
-(6 rows)
+(5 rows)
 
 --
 -- test that quals attached to an outer join have correct semantics,
commit 4b851dd9acb73943d3d07220d7bf34f152b44dc1
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 15:17:10 2023 -0500

    Teach remove_useless_result_rtes to also remove useless FromExprs.
    
    If a FromExpr has but one child, we can get rid of it even if it
    has some quals, if we can move those quals up to the parent jointree
    node.  In particular, this works for a FromExpr just below the RHS
    of a LEFT JOIN, because the quals of such a FromExpr are equivalent
    to degenerate quals of the left join.  By recursively applying this
    rule, we can guarantee that the RHS child of a left join is either
    not a FromExpr or has more than one child.
    
    The point of this transformation is not so much to simplify the join
    tree as it is to eliminate the problem for which commit 11086f2f2
    invented the delay_upper_joins mechanism.  The idea of that was
    to ensure that quals in such a FromExpr would block outer join
    rearrangement as if they were degenerate quals of the upper join.
    But after this transformation, they *are* degenerate quals of the
    upper join, and we don't need an indirect mechanism any more.
    (Note that a multi-child FromExpr isn't a problem, because that must
    represent an inner join, which can't commute with the outer join
    anyway.)
    
    This results in one visible change in regression outputs: in one test
    case, there is now an explicit constant-false join filter condition,
    which got there by being pushed up from a removed FromExpr.  We still
    detect that the child plan is dummy, but now that happens because
    populate_joinrel_with_paths pushes the knowledge back down after
    noticing that the parent left join has a constant-false join
    condition.  Since it's such a hokey case, I'm not concerned about
    the extra qual condition, and see no point in making an effort to
    eliminate it.
    
    Having done that, the delay_upper_joins flag serves no purpose any
    more and we can remove it, largely reverting 11086f2f2.  (The end
    game here is to get rid of check_outerjoin_delay altogether, but
    first we must get rid of its side effects.)  Although this patch
    doesn't make any net code savings, I think it's still an improvement
    because it replaces a fuzzily-defined action-at-a-distance flag
    with a simple and provably correct jointree transformation.

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 7d957a47a4..7918bb6f0d 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -4787,7 +4787,6 @@ compute_semi_anti_join_factors(PlannerInfo *root,
 	norm_sjinfo.commute_below = NULL;
 	/* we don't bother trying to make the remaining fields valid */
 	norm_sjinfo.lhs_strict = false;
-	norm_sjinfo.delay_upper_joins = false;
 	norm_sjinfo.semi_can_btree = false;
 	norm_sjinfo.semi_can_hash = false;
 	norm_sjinfo.semi_operators = NIL;
@@ -4956,7 +4955,6 @@ approx_tuple_count(PlannerInfo *root, JoinPath *path, List *quals)
 	sjinfo.commute_below = NULL;
 	/* we don't bother trying to make the remaining fields valid */
 	sjinfo.lhs_strict = false;
-	sjinfo.delay_upper_joins = false;
 	sjinfo.semi_can_btree = false;
 	sjinfo.semi_can_hash = false;
 	sjinfo.semi_operators = NIL;
diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 56dd1073c5..d7cb11c851 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -743,7 +743,6 @@ make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
 		sjinfo->commute_below = NULL;
 		/* we don't bother trying to make the remaining fields valid */
 		sjinfo->lhs_strict = false;
-		sjinfo->delay_upper_joins = false;
 		sjinfo->semi_can_btree = false;
 		sjinfo->semi_can_hash = false;
 		sjinfo->semi_operators = NIL;
diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index fbb652e7b0..42da62c1c6 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -170,11 +170,10 @@ join_is_removable(PlannerInfo *root, SpecialJoinInfo *sjinfo)
 	int			attroff;
 
 	/*
-	 * Must be a non-delaying left join to a single baserel, else we aren't
-	 * going to be able to do anything with it.
+	 * Must be a left join to a single baserel, else we aren't going to be
+	 * able to do anything with it.
 	 */
-	if (sjinfo->jointype != JOIN_LEFT ||
-		sjinfo->delay_upper_joins)
+	if (sjinfo->jointype != JOIN_LEFT)
 		return false;
 
 	if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
@@ -570,13 +569,10 @@ reduce_unique_semijoins(PlannerInfo *root)
 		List	   *restrictlist;
 
 		/*
-		 * Must be a non-delaying semijoin to a single baserel, else we aren't
-		 * going to be able to do anything with it.  (It's probably not
-		 * possible for delay_upper_joins to be set on a semijoin, but we
-		 * might as well check.)
+		 * Must be a semijoin to a single baserel, else we aren't going to be
+		 * able to do anything with it.
 		 */
-		if (sjinfo->jointype != JOIN_SEMI ||
-			sjinfo->delay_upper_joins)
+		if (sjinfo->jointype != JOIN_SEMI)
 			continue;
 
 		if (!bms_get_singleton_member(sjinfo->min_righthand, &innerrelid))
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 934432b9c0..c6134bc94e 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -130,8 +130,7 @@ static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									bool is_clone,
 									List **postponed_qual_list,
 									List **postponed_oj_qual_list);
-static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
-								  bool is_pushed_down);
+static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p);
 static bool check_equivalence_delay(PlannerInfo *root,
 									RestrictInfo *restrictinfo);
 static bool check_redundant_nullability_qual(PlannerInfo *root, Node *clause);
@@ -1439,8 +1438,6 @@ make_outerjoininfo(PlannerInfo *root,
 	sjinfo->commute_above_l = NULL;
 	sjinfo->commute_above_r = NULL;
 	sjinfo->commute_below = NULL;
-	/* this always starts out false */
-	sjinfo->delay_upper_joins = false;
 
 	compute_semijoin_info(root, sjinfo, clause);
 
@@ -1595,17 +1592,6 @@ make_outerjoininfo(PlannerInfo *root,
 		 * Also, we must preserve ordering anyway if we have unsafe PHVs, or
 		 * if either this join or the lower OJ is a semijoin or antijoin.
 		 *
-		 * Here, we have to consider that "our join condition" includes any
-		 * clauses that syntactically appeared above the lower OJ and below
-		 * ours; those are equivalent to degenerate clauses in our OJ and must
-		 * be treated as such.  Such clauses obviously can't reference our
-		 * LHS, and they must be non-strict for the lower OJ's RHS (else
-		 * reduce_outer_joins would have reduced the lower OJ to a plain
-		 * join).  Hence the other ways in which we handle clauses within our
-		 * join condition are not affected by them.  The net effect is
-		 * therefore sufficiently represented by the delay_upper_joins flag
-		 * saved for us by check_outerjoin_delay.
-		 *
 		 * When we don't need to preserve ordering, check to see if outer join
 		 * identity 3 applies, and if so, remove the lower OJ's ojrelid from
 		 * our min_righthand so that commutation is allowed.
@@ -1619,7 +1605,7 @@ make_outerjoininfo(PlannerInfo *root,
 				jointype == JOIN_ANTI ||
 				otherinfo->jointype == JOIN_SEMI ||
 				otherinfo->jointype == JOIN_ANTI ||
-				!otherinfo->lhs_strict || otherinfo->delay_upper_joins)
+				!otherinfo->lhs_strict)
 			{
 				/* Preserve ordering */
 				min_righthand = bms_add_members(min_righthand,
@@ -2344,8 +2330,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 
 		/* Check to see if must be delayed by lower outer join */
 		outerjoin_delayed = check_outerjoin_delay(root,
-												  &relids,
-												  false);
+												  &relids);
 
 		/*
 		 * Now force the qual to be evaluated exactly at the level of joining
@@ -2371,8 +2356,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 
 		/* Check to see if must be delayed by lower outer join */
 		outerjoin_delayed = check_outerjoin_delay(root,
-												  &relids,
-												  true);
+												  &relids);
 
 		if (outerjoin_delayed)
 		{
@@ -2583,13 +2567,10 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 /*
  * check_outerjoin_delay
  *		Detect whether a qual referencing the given relids must be delayed
- *		in application due to the presence of a lower outer join, and/or
- *		may force extra delay of higher-level outer joins.
+ *		in application due to the presence of a lower outer join.
  *
  * If the qual must be delayed, add relids to *relids_p to reflect the lowest
- * safe level for evaluating the qual, and return true.  Any extra delay for
- * higher-level joins is reflected by setting delay_upper_joins to true in
- * SpecialJoinInfo structs.
+ * safe level for evaluating the qual, and return true.
  *
  * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
  * all the rels it mentions, and (2) we are at or above any outer joins that
@@ -2614,24 +2595,10 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
  * For a non-pushed-down qual, this isn't going to determine where we place the
  * qual, but we need to determine outerjoin_delayed anyway for use later in
  * the planning process.
- *
- * Lastly, a pushed-down qual that references the nullable side of any current
- * join_info_list member and has to be evaluated above that OJ (because its
- * required relids overlap the LHS too) causes that OJ's delay_upper_joins
- * flag to be set true.  This will prevent any higher-level OJs from
- * being interchanged with that OJ, which would result in not having any
- * correct place to evaluate the qual.  (The case we care about here is a
- * sub-select WHERE clause within the RHS of some outer join.  The WHERE
- * clause must effectively be treated as a degenerate clause of that outer
- * join's condition.  Rather than trying to match such clauses with joins
- * directly, we set delay_upper_joins here, and when the upper outer join
- * is processed by make_outerjoininfo, it will refrain from allowing the
- * two OJs to commute.)
  */
 static bool
 check_outerjoin_delay(PlannerInfo *root,
-					  Relids *relids_p, /* in/out parameter */
-					  bool is_pushed_down)
+					  Relids *relids_p) /* in/out parameter */
 {
 	Relids		relids;
 	bool		outerjoin_delayed;
@@ -2669,10 +2636,6 @@ check_outerjoin_delay(PlannerInfo *root,
 					/* we'll need another iteration */
 					found_some = true;
 				}
-				/* set delay_upper_joins if needed */
-				if (is_pushed_down && sjinfo->jointype != JOIN_FULL &&
-					bms_overlap(relids, sjinfo->min_lefthand))
-					sjinfo->delay_upper_joins = true;
 			}
 		}
 	} while (found_some);
@@ -2709,12 +2672,12 @@ check_equivalence_delay(PlannerInfo *root,
 	/* must copy restrictinfo's relids to avoid changing it */
 	relids = bms_copy(restrictinfo->left_relids);
 	/* check left side does not need delay */
-	if (check_outerjoin_delay(root, &relids, true))
+	if (check_outerjoin_delay(root, &relids))
 		return false;
 
 	/* and similarly for the right side */
 	relids = bms_copy(restrictinfo->right_relids);
-	if (check_outerjoin_delay(root, &relids, true))
+	if (check_outerjoin_delay(root, &relids))
 		return false;
 
 	return true;
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 320caebd87..8674ad674d 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -1044,10 +1044,11 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 
 	/*
 	 * If we have any RTE_RESULT relations, see if they can be deleted from
-	 * the jointree.  This step is most effectively done after we've done
-	 * expression preprocessing and outer join reduction.
+	 * the jointree.  We also rely on this processing to flatten single-child
+	 * FromExprs underneath outer joins.  This step is most effectively done
+	 * after we've done expression preprocessing and outer join reduction.
 	 */
-	if (hasResultRTEs)
+	if (hasResultRTEs || hasOuterJoins)
 		remove_useless_result_rtes(root);
 
 	/*
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index 9c96a558fc..eacfb66b31 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -130,6 +130,7 @@ static void reduce_outer_joins_pass2(Node *jtnode,
 static void report_reduced_full_join(reduce_outer_joins_pass2_state *state2,
 									 int rtindex, Relids relids);
 static Node *remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
+											Node **parent_quals,
 											Relids *dropped_outer_joins);
 static int	get_result_relid(PlannerInfo *root, Node *jtnode);
 static void remove_result_refs(PlannerInfo *root, int varno, Node *newjtloc);
@@ -3085,12 +3086,31 @@ report_reduced_full_join(reduce_outer_joins_pass2_state *state2,
 /*
  * remove_useless_result_rtes
  *		Attempt to remove RTE_RESULT RTEs from the join tree.
+ *		Also, elide single-child FromExprs where possible.
  *
  * We can remove RTE_RESULT entries from the join tree using the knowledge
  * that RTE_RESULT returns exactly one row and has no output columns.  Hence,
  * if one is inner-joined to anything else, we can delete it.  Optimizations
  * are also possible for some outer-join cases, as detailed below.
  *
+ * This pass also replaces single-child FromExprs with their child node
+ * where possible.  It's appropriate to do that here and not earlier because
+ * RTE_RESULT removal might reduce a multiple-child FromExpr to have only one
+ * child.  We can remove such a FromExpr if its quals are empty, or if it's
+ * semantically valid to merge the quals into those of the parent node.
+ * While removing unnecessary join tree nodes has some micro-efficiency value,
+ * the real reason to do this is to eliminate cases where the nullable side of
+ * an outer join node is a FromExpr whose single child is another outer join.
+ * To correctly determine whether the two outer joins can commute,
+ * deconstruct_jointree() must treat any quals of such a FromExpr as being
+ * degenerate quals of the upper outer join.  The best way to do that is to
+ * make them actually *be* quals of the upper join, by dropping the FromExpr
+ * and hoisting the quals up into the upper join's quals.  (Note that there is
+ * no hazard when the intermediate FromExpr has multiple children, since then
+ * it represents an inner join that cannot commute with the upper outer join.)
+ * As long as we have to do that, we might as well elide such FromExprs
+ * everywhere.
+ *
  * Some of these optimizations depend on recognizing empty (constant-true)
  * quals for FromExprs and JoinExprs.  That makes it useful to apply this
  * optimization pass after expression preprocessing, since that will have
@@ -3131,6 +3151,7 @@ remove_useless_result_rtes(PlannerInfo *root)
 	root->parse->jointree = (FromExpr *)
 		remove_useless_results_recurse(root,
 									   (Node *) root->parse->jointree,
+									   NULL,
 									   &dropped_outer_joins);
 	/* We should still have a FromExpr */
 	Assert(IsA(root->parse->jointree, FromExpr));
@@ -3184,9 +3205,14 @@ remove_useless_result_rtes(PlannerInfo *root)
  * This recursively processes the jointree and returns a modified jointree.
  * In addition, the RT indexes of any removed outer-join nodes are added to
  * *dropped_outer_joins.
+ *
+ * jtnode is the current jointree node.  If it could be valid to merge
+ * its quals into those of the parent node, parent_quals should point to
+ * the parent's quals list; otherwise, pass NULL for parent_quals.
  */
 static Node *
 remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
+							   Node **parent_quals,
 							   Relids *dropped_outer_joins)
 {
 	Assert(jtnode != NULL);
@@ -3214,8 +3240,9 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 			Node	   *child = (Node *) lfirst(cell);
 			int			varno;
 
-			/* Recursively transform child ... */
+			/* Recursively transform child, allowing it to push up quals ... */
 			child = remove_useless_results_recurse(root, child,
+												   &f->quals,
 												   dropped_outer_joins);
 			/* ... and stick it back into the tree */
 			lfirst(cell) = child;
@@ -3249,25 +3276,54 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 		}
 
 		/*
-		 * If we're not at the top of the jointree, it's valid to simplify a
-		 * degenerate FromExpr into its single child.  (At the top, we must
-		 * keep the FromExpr since Query.jointree is required to point to a
-		 * FromExpr.)
+		 * If the FromExpr now has only one child, see if we can elide it.
+		 * This is always valid if there are no quals, except at the top of
+		 * the jointree (since Query.jointree is required to point to a
+		 * FromExpr).  Otherwise, we can do it if we can push the quals up to
+		 * the parent node.
+		 *
+		 * Note: while it would not be terribly hard to generalize this
+		 * transformation to merge multi-child FromExprs into their parent
+		 * FromExpr, that risks making the parent join too expensive to plan.
+		 * We leave it to later processing to decide heuristically whether
+		 * that's a good idea.  Pulling up a single child is always OK,
+		 * however.
 		 */
-		if (f != root->parse->jointree &&
-			f->quals == NULL &&
-			list_length(f->fromlist) == 1)
+		if (list_length(f->fromlist) == 1 &&
+			f != root->parse->jointree &&
+			(f->quals == NULL || parent_quals != NULL))
+		{
+			/*
+			 * Merge any quals up to parent.  They should be in implicit-AND
+			 * format by now, so we just need to concatenate lists.  Put the
+			 * child quals at the front, on the grounds that they should
+			 * nominally be evaluated earlier.
+			 */
+			if (f->quals != NULL)
+				*parent_quals = (Node *)
+					list_concat(castNode(List, f->quals),
+								castNode(List, *parent_quals));
 			return (Node *) linitial(f->fromlist);
+		}
 	}
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
 		int			varno;
 
-		/* First, recurse */
+		/*
+		 * First, recurse.  We can accept pushed-up FromExpr quals from either
+		 * child if the jointype is INNER, and we can accept them from the RHS
+		 * child if the jointype is LEFT.
+		 */
 		j->larg = remove_useless_results_recurse(root, j->larg,
+												 (j->jointype == JOIN_INNER) ?
+												 &j->quals : NULL,
 												 dropped_outer_joins);
 		j->rarg = remove_useless_results_recurse(root, j->rarg,
+												 (j->jointype == JOIN_INNER ||
+												  j->jointype == JOIN_LEFT) ?
+												 &j->quals : NULL,
 												 dropped_outer_joins);
 
 		/* Apply join-type-specific optimization rules */
@@ -3278,9 +3334,9 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 				/*
 				 * An inner join is equivalent to a FromExpr, so if either
 				 * side was simplified to an RTE_RESULT rel, we can replace
-				 * the join with a FromExpr with just the other side; and if
-				 * the qual is empty (JOIN ON TRUE) then we can omit the
-				 * FromExpr as well.
+				 * the join with a FromExpr with just the other side.
+				 * Furthermore, we can elide that FromExpr according to the
+				 * same rules as above.
 				 *
 				 * Just as in the FromExpr case, we can't simplify if the
 				 * other input rel references any PHVs that are marked as to
@@ -3295,20 +3351,34 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 					!find_dependent_phvs_in_jointree(root, j->rarg, varno))
 				{
 					remove_result_refs(root, varno, j->rarg);
-					if (j->quals)
+					if (j->quals != NULL && parent_quals == NULL)
 						jtnode = (Node *)
 							makeFromExpr(list_make1(j->rarg), j->quals);
 					else
+					{
+						/* Merge any quals up to parent */
+						if (j->quals != NULL)
+							*parent_quals = (Node *)
+								list_concat(castNode(List, j->quals),
+											castNode(List, *parent_quals));
 						jtnode = j->rarg;
+					}
 				}
 				else if ((varno = get_result_relid(root, j->rarg)) != 0)
 				{
 					remove_result_refs(root, varno, j->larg);
-					if (j->quals)
+					if (j->quals != NULL && parent_quals == NULL)
 						jtnode = (Node *)
 							makeFromExpr(list_make1(j->larg), j->quals);
 					else
+					{
+						/* Merge any quals up to parent */
+						if (j->quals != NULL)
+							*parent_quals = (Node *)
+								list_concat(castNode(List, j->quals),
+											castNode(List, *parent_quals));
 						jtnode = j->larg;
+					}
 				}
 				break;
 			case JOIN_LEFT:
@@ -3346,8 +3416,9 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 				/*
 				 * We may simplify this case if the RHS is an RTE_RESULT; the
 				 * join qual becomes effectively just a filter qual for the
-				 * LHS, since we should either return the LHS row or not.  For
-				 * simplicity we inject the filter qual into a new FromExpr.
+				 * LHS, since we should either return the LHS row or not.  The
+				 * filter clause must go into a new FromExpr if we can't push
+				 * it up to the parent.
 				 *
 				 * There is a fine point about PHVs that are supposed to be
 				 * evaluated at the RHS.  Such PHVs could only appear in the
@@ -3365,11 +3436,18 @@ remove_useless_results_recurse(PlannerInfo *root, Node *jtnode,
 				{
 					Assert(j->rtindex == 0);
 					remove_result_refs(root, varno, j->larg);
-					if (j->quals)
+					if (j->quals != NULL && parent_quals == NULL)
 						jtnode = (Node *)
 							makeFromExpr(list_make1(j->larg), j->quals);
 					else
+					{
+						/* Merge any quals up to parent */
+						if (j->quals != NULL)
+							*parent_quals = (Node *)
+								list_concat(castNode(List, j->quals),
+											castNode(List, *parent_quals));
 						jtnode = j->larg;
+					}
 				}
 				break;
 			case JOIN_FULL:
diff --git a/src/backend/optimizer/util/orclauses.c b/src/backend/optimizer/util/orclauses.c
index e8972cd759..0c10646f40 100644
--- a/src/backend/optimizer/util/orclauses.c
+++ b/src/backend/optimizer/util/orclauses.c
@@ -338,7 +338,6 @@ consider_new_or_clause(PlannerInfo *root, RelOptInfo *rel,
 		sjinfo.commute_below = NULL;
 		/* we don't bother trying to make the remaining fields valid */
 		sjinfo.lhs_strict = false;
-		sjinfo.delay_upper_joins = false;
 		sjinfo.semi_can_btree = false;
 		sjinfo.semi_can_hash = false;
 		sjinfo.semi_operators = NIL;
diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index af10dbd124..8492a583dd 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -331,10 +331,7 @@ update_placeholder_eval_levels(PlannerInfo *root, SpecialJoinInfo *new_sjinfo)
 
 		/*
 		 * Check for delays due to lower outer joins.  This is the same logic
-		 * as in check_outerjoin_delay in initsplan.c, except that we don't
-		 * have anything to do with the delay_upper_joins flags; delay of
-		 * upper outer joins will be handled later, based on the eval_at
-		 * values we compute now.
+		 * as in check_outerjoin_delay in initsplan.c.
 		 */
 		eval_at = phinfo->ph_eval_at;
 
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 38a6f1adc8..56df0e92eb 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2774,12 +2774,6 @@ typedef struct PlaceHolderVar
  * upper-level outer joins even if it appears in their RHS).  We don't bother
  * to set lhs_strict for FULL JOINs, however.
  *
- * delay_upper_joins is set true if we detect a pushed-down clause that has
- * to be evaluated after this join is formed (because it references the RHS).
- * Any outer joins that have such a clause and this join in their RHS cannot
- * commute with this join, because that would leave noplace to check the
- * pushed-down clause.  (We don't track this for FULL JOINs, either.)
- *
  * For a semijoin, we also extract the join operators and their RHS arguments
  * and set semi_operators, semi_rhs_exprs, semi_can_btree, and semi_can_hash.
  * This is done in support of possibly unique-ifying the RHS, so we don't
@@ -2794,8 +2788,8 @@ typedef struct PlaceHolderVar
  * not allowed within join_info_list.  We also create transient
  * SpecialJoinInfos with jointype == JOIN_INNER for outer joins, since for
  * cost estimation purposes it is sometimes useful to know the join size under
- * plain innerjoin semantics.  Note that lhs_strict, delay_upper_joins, and
- * of course the semi_xxx fields are not set meaningfully within such structs.
+ * plain innerjoin semantics.  Note that lhs_strict and the semi_xxx fields
+ * are not set meaningfully within such structs.
  */
 #ifndef HAVE_SPECIALJOININFO_TYPEDEF
 typedef struct SpecialJoinInfo SpecialJoinInfo;
@@ -2817,7 +2811,6 @@ struct SpecialJoinInfo
 	Relids		commute_above_r;	/* commuting OJs above this one, if RHS */
 	Relids		commute_below;	/* commuting OJs below this one */
 	bool		lhs_strict;		/* joinclause is strict for some LHS rel */
-	bool		delay_upper_joins;	/* can't commute with upper RHS */
 	/* Remaining fields are set only for JOIN_SEMI jointype: */
 	bool		semi_can_btree; /* true if semi_operators are all btree */
 	bool		semi_can_hash;	/* true if semi_operators are all hash */
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 6338d080d9..d2874c1cad 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -6048,12 +6048,13 @@ select * from int8_tbl i8 left join lateral
 --------------------------------------
  Nested Loop Left Join
    Output: i8.q1, i8.q2, f1, (i8.q2)
+   Join Filter: false
    ->  Seq Scan on public.int8_tbl i8
          Output: i8.q1, i8.q2
    ->  Result
          Output: f1, i8.q2
          One-Time Filter: false
-(7 rows)
+(8 rows)
 
 explain (verbose, costs off)
 select * from int8_tbl i8 left join lateral
commit 1ea6ac291281a805b5ae70e5835883161179ae1e
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 15:22:26 2023 -0500

    Remove the outerjoin_delayed mechanism.
    
    We needed this before to prevent quals from getting evaluated below
    outer joins that should null some of their vars.  Now that we consider
    varnullingrels while placing quals, that's taken care of
    automatically, so throw the whole thing away.
    
    This results in one cosmetic change in the regression test outputs,
    where clauses that were not previously considered to be
    EquivalenceClass candidates are now treated as ECs, and the EC
    machinery chooses to emit an equivalent but not identical set of
    clauses.

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index d95e70dfce..f5926ab89d 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -6522,7 +6522,6 @@ foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
 									  expr,
 									  true,
 									  false,
-									  false,
 									  root->qual_security_level,
 									  grouped_rel->relids,
 									  NULL);
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index f0eadbcfb9..fe82b55445 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -200,7 +200,6 @@ process_equivalence(PlannerInfo *root,
 				make_restrictinfo(root,
 								  (Expr *) ntest,
 								  restrictinfo->is_pushed_down,
-								  restrictinfo->outerjoin_delayed,
 								  restrictinfo->pseudoconstant,
 								  restrictinfo->security_level,
 								  NULL,
@@ -1144,11 +1143,8 @@ generate_base_implied_equalities_const(PlannerInfo *root,
 	{
 		RestrictInfo *restrictinfo = (RestrictInfo *) linitial(ec->ec_sources);
 
-		if (bms_membership(restrictinfo->required_relids) != BMS_MULTIPLE)
-		{
-			distribute_restrictinfo_to_rels(root, restrictinfo);
-			return;
-		}
+		distribute_restrictinfo_to_rels(root, restrictinfo);
+		return;
 	}
 
 	/*
@@ -1959,15 +1955,6 @@ create_join_clause(PlannerInfo *root,
  * seen as a clauseless join and avoided during join order searching.
  * We handle this by generating a constant-TRUE clause that is marked with
  * required_relids that make it a join between the correct relations.
- *
- * Outer join clauses that are marked outerjoin_delayed are special: this
- * condition means that one or both VARs might go to null due to a lower
- * outer join.  We can still push a constant through the clause, but only
- * if its operator is strict; and we *have to* throw the clause back into
- * regular joinclause processing.  By keeping the strict join clause,
- * we ensure that any null-extended rows that are mistakenly generated due
- * to suppressing rows not matching the constant will be rejected at the
- * upper outer join.  (This doesn't work for full-join clauses.)
  */
 void
 reconsider_outer_join_clauses(PlannerInfo *root)
@@ -1997,7 +1984,6 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				rinfo = make_restrictinfo(root,
 										  (Expr *) makeBoolConst(true, false),
 										  true, /* is_pushed_down */
-										  false,	/* outerjoin_delayed */
 										  false,	/* pseudoconstant */
 										  0,	/* security_level */
 										  rinfo->required_relids,
@@ -2023,7 +2009,6 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				rinfo = make_restrictinfo(root,
 										  (Expr *) makeBoolConst(true, false),
 										  true, /* is_pushed_down */
-										  false,	/* outerjoin_delayed */
 										  false,	/* pseudoconstant */
 										  0,	/* security_level */
 										  rinfo->required_relids,
@@ -2049,7 +2034,6 @@ reconsider_outer_join_clauses(PlannerInfo *root)
 				rinfo = make_restrictinfo(root,
 										  (Expr *) makeBoolConst(true, false),
 										  true, /* is_pushed_down */
-										  false,	/* outerjoin_delayed */
 										  false,	/* pseudoconstant */
 										  0,	/* security_level */
 										  rinfo->required_relids,
@@ -2104,10 +2088,6 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 	opno = ((OpExpr *) rinfo->clause)->opno;
 	collation = ((OpExpr *) rinfo->clause)->inputcollid;
 
-	/* If clause is outerjoin_delayed, operator must be strict */
-	if (rinfo->outerjoin_delayed && !op_strict(opno))
-		return false;
-
 	/* Extract needed info from the clause */
 	op_input_types(opno, &left_type, &right_type);
 	if (outer_on_left)
@@ -2224,10 +2204,6 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 				right_relids;
 	ListCell   *lc1;
 
-	/* Can't use an outerjoin_delayed clause here */
-	if (rinfo->outerjoin_delayed)
-		return false;
-
 	/* Extract needed info from the clause */
 	Assert(is_opclause(rinfo->clause));
 	opno = ((OpExpr *) rinfo->clause)->opno;
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index c6134bc94e..0f4163bffd 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -130,9 +130,6 @@ static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 									bool is_clone,
 									List **postponed_qual_list,
 									List **postponed_oj_qual_list);
-static bool check_outerjoin_delay(PlannerInfo *root, Relids *relids_p);
-static bool check_equivalence_delay(PlannerInfo *root,
-									RestrictInfo *restrictinfo);
 static bool check_redundant_nullability_qual(PlannerInfo *root, Node *clause);
 static void check_mergejoinable(RestrictInfo *restrictinfo);
 static void check_hashjoinable(RestrictInfo *restrictinfo);
@@ -738,15 +735,6 @@ create_lateral_join_info(PlannerInfo *root)
  * A sub-joinlist represents a subproblem to be planned separately. Currently
  * sub-joinlists arise only from FULL OUTER JOIN or when collapsing of
  * subproblems is stopped by join_collapse_limit or from_collapse_limit.
- *
- * NOTE: when dealing with inner joins, it is appropriate to let a qual clause
- * be evaluated at the lowest level where all the variables it mentions are
- * available.  However, we cannot push a qual down into the nullable side(s)
- * of an outer join since the qual might eliminate matching rows and cause a
- * NULL row to be incorrectly emitted by the join.  Therefore, we artificially
- * OR the minimum-relids of such an outer join into the required_relids of
- * clauses appearing above it.  This forces those clauses to be delayed until
- * application of the outer join (or maybe even higher in the join tree).
  */
 List *
 deconstruct_jointree(PlannerInfo *root)
@@ -758,9 +746,8 @@ deconstruct_jointree(PlannerInfo *root)
 
 	/*
 	 * After this point, no more PlaceHolderInfos may be made, because
-	 * make_outerjoininfo and update_placeholder_eval_levels require all
-	 * active placeholders to be present in root->placeholder_list while we
-	 * crawl up the join tree.
+	 * make_outerjoininfo requires all active placeholders to be present in
+	 * root->placeholder_list while we crawl up the join tree.
 	 */
 	root->placeholdersFrozen = true;
 
@@ -798,31 +785,12 @@ deconstruct_jointree(PlannerInfo *root)
 	 */
 	if (root->join_info_list)
 	{
-		/*
-		 * XXX hack: when we call distribute_qual_to_rels to process one of
-		 * these clauses, neither the owning SpecialJoinInfo nor any later
-		 * ones can appear in root->join_info_list, else the wrong things will
-		 * happen.  Fake it out by emptying join_info_list and rebuilding it
-		 * as we go. This works because join_info_list is only appended to
-		 * during deconstruct_distribute, so we know we are examining
-		 * SpecialJoinInfos bottom-up, just like the first time.  We can get
-		 * rid of this hack later, after fixing things so that
-		 * distribute_qual_to_rels doesn't have that requirement about
-		 * join_info_list.
-		 */
-		root->join_info_list = NIL;
-
 		foreach(lc, item_list)
 		{
 			JoinTreeItem *jtitem = (JoinTreeItem *) lfirst(lc);
 
 			if (jtitem->oj_joinclauses != NIL)
 				deconstruct_distribute_oj_quals(root, item_list, jtitem);
-
-			/* XXX Rest of hack: rebuild join_info_list as we go */
-			if (jtitem->sjinfo)
-				root->join_info_list = lappend(root->join_info_list,
-											   jtitem->sjinfo);
 		}
 	}
 
@@ -1265,11 +1233,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 
 		/* And add the SpecialJoinInfo to join_info_list */
 		if (sjinfo)
-		{
 			root->join_info_list = lappend(root->join_info_list, sjinfo);
-			/* Each time we do that, recheck placeholder eval levels */
-			update_placeholder_eval_levels(root, sjinfo);
-		}
 	}
 	else
 	{
@@ -2155,8 +2119,8 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
  * level, which will be ojscope not necessarily qualscope.
  *
  * At the time this is called, root->join_info_list must contain entries for
- * all and only those special joins that are syntactically below this qual;
- * in particular, the passed-in SpecialJoinInfo isn't yet in that list.
+ * at least those special joins that are syntactically below this qual.
+ * (We now need that only for detection of redundant IS NULL quals.)
  */
 static void
 distribute_qual_to_rels(PlannerInfo *root, Node *clause,
@@ -2174,7 +2138,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 {
 	Relids		relids;
 	bool		is_pushed_down;
-	bool		outerjoin_delayed;
 	bool		pseudoconstant = false;
 	bool		maybe_equivalence;
 	bool		maybe_outer_join;
@@ -2328,19 +2291,12 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		maybe_equivalence = false;
 		maybe_outer_join = true;
 
-		/* Check to see if must be delayed by lower outer join */
-		outerjoin_delayed = check_outerjoin_delay(root,
-												  &relids);
-
 		/*
 		 * Now force the qual to be evaluated exactly at the level of joining
 		 * corresponding to the outer join.  We cannot let it get pushed down
 		 * into the nonnullable side, since then we'd produce no output rows,
 		 * rather than the intended single null-extended row, for any
 		 * nonnullable-side rows failing the qual.
-		 *
-		 * (Do this step after calling check_outerjoin_delay, because that
-		 * trashes relids.)
 		 */
 		Assert(ojscope);
 		relids = ojscope;
@@ -2354,32 +2310,16 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		 */
 		is_pushed_down = true;
 
-		/* Check to see if must be delayed by lower outer join */
-		outerjoin_delayed = check_outerjoin_delay(root,
-												  &relids);
-
-		if (outerjoin_delayed)
-		{
-			/* Should still be a subset of current scope ... */
-			Assert(root->hasLateralRTEs || bms_is_subset(relids, qualscope));
-			Assert(ojscope == NULL || bms_is_subset(relids, ojscope));
-
-			/*
-			 * Because application of the qual will be delayed by outer join,
-			 * we mustn't assume its vars are equal everywhere.
-			 */
-			maybe_equivalence = false;
+		/*
+		 * It's possible that this is an IS NULL clause that's redundant with
+		 * a lower antijoin; if so we can just discard it.  We need not test
+		 * in any of the other cases, because this will only be possible for
+		 * pushed-down clauses.
+		 */
+		if (check_redundant_nullability_qual(root, clause))
+			return;
 
-			/*
-			 * It's possible that this is an IS NULL clause that's redundant
-			 * with a lower antijoin; if so we can just discard it.  We need
-			 * not test in any of the other cases, because this will only be
-			 * possible for pushed-down, delayed clauses.
-			 */
-			if (check_redundant_nullability_qual(root, clause))
-				return;
-		}
-		else if (!allow_equivalence)
+		if (!allow_equivalence)
 		{
 			/* Caller says it mustn't become an equivalence class */
 			maybe_equivalence = false;
@@ -2387,8 +2327,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		else
 		{
 			/*
-			 * Qual is not delayed by any lower outer-join restriction, so we
-			 * can consider feeding it to the equivalence machinery. However,
+			 * Consider feeding qual to the equivalence machinery.  However,
 			 * if it's itself within an outer-join clause, treat it as though
 			 * it appeared below that outer join (note that we can only get
 			 * here when the clause references only nullable-side rels).
@@ -2411,7 +2350,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	restrictinfo = make_restrictinfo(root,
 									 (Expr *) clause,
 									 is_pushed_down,
-									 outerjoin_delayed,
 									 pseudoconstant,
 									 security_level,
 									 relids,
@@ -2463,6 +2401,8 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	check_mergejoinable(restrictinfo);
 
 	/*
+	 * XXX rewrite:
+	 *
 	 * If it is a true equivalence clause, send it to the EquivalenceClass
 	 * machinery.  We do *not* attach it directly to any restriction or join
 	 * lists.  The EC code will propagate it to the appropriate places later.
@@ -2498,8 +2438,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	{
 		if (maybe_equivalence)
 		{
-			if (check_equivalence_delay(root, restrictinfo) &&
-				process_equivalence(root, &restrictinfo, below_outer_join))
+			if (process_equivalence(root, &restrictinfo, below_outer_join))
 				return;
 			/* EC rejected it, so set left_ec/right_ec the hard way ... */
 			if (restrictinfo->mergeopfamilies)	/* EC might have changed this */
@@ -2564,125 +2503,6 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	distribute_restrictinfo_to_rels(root, restrictinfo);
 }
 
-/*
- * check_outerjoin_delay
- *		Detect whether a qual referencing the given relids must be delayed
- *		in application due to the presence of a lower outer join.
- *
- * If the qual must be delayed, add relids to *relids_p to reflect the lowest
- * safe level for evaluating the qual, and return true.
- *
- * For an is_pushed_down qual, we can evaluate the qual as soon as (1) we have
- * all the rels it mentions, and (2) we are at or above any outer joins that
- * can null any of these rels and are below the syntactic location of the
- * given qual.  We must enforce (2) because pushing down such a clause below
- * the OJ might cause the OJ to emit null-extended rows that should not have
- * been formed, or that should have been rejected by the clause.  (This is
- * only an issue for non-strict quals, since if we can prove a qual mentioning
- * only nullable rels is strict, we'd have reduced the outer join to an inner
- * join in reduce_outer_joins().)
- *
- * To enforce (2), scan the join_info_list and merge the required-relid sets of
- * any such OJs into the clause's own reference list.  At the time we are
- * called, the join_info_list contains only outer joins below this qual.  We
- * have to repeat the scan until no new relids get added; this ensures that
- * the qual is suitably delayed regardless of the order in which OJs get
- * executed.  As an example, if we have one OJ with LHS=A, RHS=B, and one with
- * LHS=B, RHS=C, it is implied that these can be done in either order; if the
- * B/C join is done first then the join to A can null C, so a qual actually
- * mentioning only C cannot be applied below the join to A.
- *
- * For a non-pushed-down qual, this isn't going to determine where we place the
- * qual, but we need to determine outerjoin_delayed anyway for use later in
- * the planning process.
- */
-static bool
-check_outerjoin_delay(PlannerInfo *root,
-					  Relids *relids_p) /* in/out parameter */
-{
-	Relids		relids;
-	bool		outerjoin_delayed;
-	bool		found_some;
-
-	/* fast path if no special joins */
-	if (root->join_info_list == NIL)
-		return false;
-
-	/* must copy relids because we need the original value at the end */
-	relids = bms_copy(*relids_p);
-	outerjoin_delayed = false;
-	do
-	{
-		ListCell   *l;
-
-		found_some = false;
-		foreach(l, root->join_info_list)
-		{
-			SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
-
-			/* do we reference any nullable rels of this OJ? */
-			if (bms_overlap(relids, sjinfo->min_righthand) ||
-				(sjinfo->jointype == JOIN_FULL &&
-				 bms_overlap(relids, sjinfo->min_lefthand)))
-			{
-				/* yes; have we included all its rels in relids? */
-				if (!bms_is_subset(sjinfo->min_lefthand, relids) ||
-					!bms_is_subset(sjinfo->min_righthand, relids))
-				{
-					/* no, so add them in */
-					relids = bms_add_members(relids, sjinfo->min_lefthand);
-					relids = bms_add_members(relids, sjinfo->min_righthand);
-					outerjoin_delayed = true;
-					/* we'll need another iteration */
-					found_some = true;
-				}
-			}
-		}
-	} while (found_some);
-
-	/* replace *relids_p */
-	bms_free(*relids_p);
-	*relids_p = relids;
-	return outerjoin_delayed;
-}
-
-/*
- * check_equivalence_delay
- *		Detect whether a potential equivalence clause is rendered unsafe
- *		by outer-join-delay considerations.  Return true if it's safe.
- *
- * The initial tests in distribute_qual_to_rels will consider a mergejoinable
- * clause to be a potential equivalence clause if it is not outerjoin_delayed.
- * But since the point of equivalence processing is that we will recombine the
- * two sides of the clause with others, we have to check that each side
- * satisfies the not-outerjoin_delayed condition on its own; otherwise it might
- * not be safe to evaluate everywhere we could place a derived equivalence
- * condition.
- */
-static bool
-check_equivalence_delay(PlannerInfo *root,
-						RestrictInfo *restrictinfo)
-{
-	Relids		relids;
-
-	/* fast path if no special joins */
-	if (root->join_info_list == NIL)
-		return true;
-
-	/* must copy restrictinfo's relids to avoid changing it */
-	relids = bms_copy(restrictinfo->left_relids);
-	/* check left side does not need delay */
-	if (check_outerjoin_delay(root, &relids))
-		return false;
-
-	/* and similarly for the right side */
-	relids = bms_copy(restrictinfo->right_relids);
-	if (check_outerjoin_delay(root, &relids))
-		return false;
-
-	return true;
-}
-
 /*
  * check_redundant_nullability_qual
  *	  Check to see if the qual is an IS NULL qual that is redundant with
@@ -2697,25 +2517,33 @@ static bool
 check_redundant_nullability_qual(PlannerInfo *root, Node *clause)
 {
 	Var		   *forced_null_var;
-	Index		forced_null_rel;
 	ListCell   *lc;
 
 	/* Check for IS NULL, and identify the Var forced to NULL */
 	forced_null_var = find_forced_null_var(clause);
 	if (forced_null_var == NULL)
 		return false;
-	forced_null_rel = forced_null_var->varno;
 
 	/*
 	 * If the Var comes from the nullable side of a lower antijoin, the IS
-	 * NULL condition is necessarily true.
+	 * NULL condition is necessarily true.  If it's not nulled by anything,
+	 * there is no point in searching the join_info_list.  Otherwise, we need
+	 * to find out whether the nulling rel is an antijoin.
 	 */
+	if (forced_null_var->varnullingrels == NULL)
+		return false;
+
 	foreach(lc, root->join_info_list)
 	{
 		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
 
-		if (sjinfo->jointype == JOIN_ANTI &&
-			bms_is_member(forced_null_rel, sjinfo->syn_righthand))
+		/*
+		 * This test will not succeed if sjinfo->ojrelid is zero, which is
+		 * possible for an antijoin that was converted from a semijoin; but in
+		 * such a case the Var couldn't have come from its nullable side.
+		 */
+		if (sjinfo->jointype == JOIN_ANTI && sjinfo->ojrelid != 0 &&
+			bms_is_member(sjinfo->ojrelid, forced_null_var->varnullingrels))
 			return true;
 	}
 
@@ -2907,7 +2735,6 @@ process_implied_equality(PlannerInfo *root,
 	restrictinfo = make_restrictinfo(root,
 									 (Expr *) clause,
 									 true,	/* is_pushed_down */
-									 false, /* outerjoin_delayed */
 									 pseudoconstant,
 									 security_level,
 									 relids,
@@ -2999,7 +2826,6 @@ build_implied_join_equality(PlannerInfo *root,
 	restrictinfo = make_restrictinfo(root,
 									 clause,
 									 true,	/* is_pushed_down */
-									 false, /* outerjoin_delayed */
 									 false, /* pseudoconstant */
 									 security_level,	/* security_level */
 									 qualscope, /* required_relids */
@@ -3071,8 +2897,7 @@ match_foreign_keys_to_quals(PlannerInfo *root)
 		 * Note: for simple inner joins, any match should be in an eclass.
 		 * "Loose" quals that syntactically match an FK equality must have
 		 * been rejected for EC status because they are outer-join quals or
-		 * similar.  We can still consider them to match the FK if they are
-		 * not outerjoin_delayed.
+		 * similar.  We can still consider them to match the FK.
 		 */
 		for (colno = 0; colno < fkinfo->nkeys; colno++)
 		{
@@ -3107,10 +2932,6 @@ match_foreign_keys_to_quals(PlannerInfo *root)
 				Var		   *leftvar;
 				Var		   *rightvar;
 
-				/* Ignore outerjoin-delayed clauses */
-				if (rinfo->outerjoin_delayed)
-					continue;
-
 				/* Only binary OpExprs are useful for consideration */
 				if (!IsA(clause, OpExpr) ||
 					list_length(clause->args) != 2)
diff --git a/src/backend/optimizer/util/inherit.c b/src/backend/optimizer/util/inherit.c
index 7842baea49..bae9688e46 100644
--- a/src/backend/optimizer/util/inherit.c
+++ b/src/backend/optimizer/util/inherit.c
@@ -894,7 +894,6 @@ apply_child_basequals(PlannerInfo *root, RelOptInfo *parentrel,
 								 make_restrictinfo(root,
 												   (Expr *) onecq,
 												   rinfo->is_pushed_down,
-												   rinfo->outerjoin_delayed,
 												   pseudoconstant,
 												   rinfo->security_level,
 												   NULL, NULL));
@@ -930,7 +929,7 @@ apply_child_basequals(PlannerInfo *root, RelOptInfo *parentrel,
 				/* not likely that we'd see constants here, so no check */
 				childquals = lappend(childquals,
 									 make_restrictinfo(root, qual,
-													   true, false, false,
+													   true, false,
 													   security_level,
 													   NULL, NULL));
 				cq_min_security = Min(cq_min_security, security_level);
diff --git a/src/backend/optimizer/util/orclauses.c b/src/backend/optimizer/util/orclauses.c
index 0c10646f40..85ecdfc14f 100644
--- a/src/backend/optimizer/util/orclauses.c
+++ b/src/backend/optimizer/util/orclauses.c
@@ -267,7 +267,6 @@ consider_new_or_clause(PlannerInfo *root, RelOptInfo *rel,
 								 orclause,
 								 true,
 								 false,
-								 false,
 								 join_or_rinfo->security_level,
 								 NULL,
 								 NULL);
diff --git a/src/backend/optimizer/util/placeholder.c b/src/backend/optimizer/util/placeholder.c
index 8492a583dd..9c6cb5eba7 100644
--- a/src/backend/optimizer/util/placeholder.c
+++ b/src/backend/optimizer/util/placeholder.c
@@ -134,7 +134,6 @@ find_placeholder_info(PlannerInfo *root, PlaceHolderVar *phv)
 		phinfo->ph_eval_at = bms_copy(phv->phrels);
 		Assert(!bms_is_empty(phinfo->ph_eval_at));
 	}
-	/* ph_eval_at may change later, see update_placeholder_eval_levels */
 	phinfo->ph_needed = NULL;	/* initially it's unused */
 	/* for the moment, estimate width using just the datatype info */
 	phinfo->ph_width = get_typavgwidth(exprType((Node *) phv->phexpr),
@@ -284,99 +283,6 @@ find_placeholders_in_expr(PlannerInfo *root, Node *expr)
 	list_free(vars);
 }
 
-/*
- * update_placeholder_eval_levels
- *		Adjust the target evaluation levels for placeholders
- *
- * The initial eval_at level set by find_placeholder_info was the set of
- * rels used in the placeholder's expression (or the whole subselect below
- * the placeholder's syntactic location, if the expr is variable-free).
- * If the query contains any outer joins that can null any of those rels,
- * we must delay evaluation to above those joins.
- *
- * We repeat this operation each time we add another outer join to
- * root->join_info_list.  It's somewhat annoying to have to do that, but
- * since we don't have very much information on the placeholders' locations,
- * it's hard to avoid.  Each placeholder's eval_at level must be correct
- * by the time it starts to figure in outer-join delay decisions for higher
- * outer joins.
- *
- * In future we might want to put additional policy/heuristics here to
- * try to determine an optimal evaluation level.  The current rules will
- * result in evaluation at the lowest possible level.  However, pushing a
- * placeholder eval up the tree is likely to further constrain evaluation
- * order for outer joins, so it could easily be counterproductive; and we
- * don't have enough information at this point to make an intelligent choice.
- */
-void
-update_placeholder_eval_levels(PlannerInfo *root, SpecialJoinInfo *new_sjinfo)
-{
-	ListCell   *lc1;
-
-	foreach(lc1, root->placeholder_list)
-	{
-		PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc1);
-		Relids		syn_level = phinfo->ph_var->phrels;
-		Relids		eval_at;
-		bool		found_some;
-		ListCell   *lc2;
-
-		/*
-		 * We don't need to do any work on this placeholder unless the
-		 * newly-added outer join is syntactically beneath its location.
-		 */
-		if (!bms_is_subset(new_sjinfo->syn_lefthand, syn_level) ||
-			!bms_is_subset(new_sjinfo->syn_righthand, syn_level))
-			continue;
-
-		/*
-		 * Check for delays due to lower outer joins.  This is the same logic
-		 * as in check_outerjoin_delay in initsplan.c.
-		 */
-		eval_at = phinfo->ph_eval_at;
-
-		do
-		{
-			found_some = false;
-			foreach(lc2, root->join_info_list)
-			{
-				SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc2);
-
-				/* disregard joins not within the PHV's sub-select */
-				if (!bms_is_subset(sjinfo->syn_lefthand, syn_level) ||
-					!bms_is_subset(sjinfo->syn_righthand, syn_level))
-					continue;
-
-				/* do we reference any nullable rels of this OJ? */
-				if (bms_overlap(eval_at, sjinfo->min_righthand) ||
-					(sjinfo->jointype == JOIN_FULL &&
-					 bms_overlap(eval_at, sjinfo->min_lefthand)))
-				{
-					/* yes; have we included all its rels in eval_at? */
-					if (!bms_is_subset(sjinfo->min_lefthand, eval_at) ||
-						!bms_is_subset(sjinfo->min_righthand, eval_at))
-					{
-						/* no, so add them in */
-						eval_at = bms_add_members(eval_at,
-												  sjinfo->min_lefthand);
-						eval_at = bms_add_members(eval_at,
-												  sjinfo->min_righthand);
-						if (sjinfo->ojrelid)
-							eval_at = bms_add_member(eval_at, sjinfo->ojrelid);
-						/* we'll need another iteration */
-						found_some = true;
-					}
-				}
-			}
-		} while (found_some);
-
-		/* Can't move the PHV's eval_at level to above its syntactic level */
-		Assert(bms_is_subset(eval_at, syn_level));
-
-		phinfo->ph_eval_at = eval_at;
-	}
-}
-
 /*
  * fix_placeholder_input_needed_levels
  *		Adjust the "needed at" levels for placeholder inputs
diff --git a/src/backend/optimizer/util/restrictinfo.c b/src/backend/optimizer/util/restrictinfo.c
index aafd74c7d2..63d41486bc 100644
--- a/src/backend/optimizer/util/restrictinfo.c
+++ b/src/backend/optimizer/util/restrictinfo.c
@@ -25,7 +25,6 @@ static RestrictInfo *make_restrictinfo_internal(PlannerInfo *root,
 												Expr *clause,
 												Expr *orclause,
 												bool is_pushed_down,
-												bool outerjoin_delayed,
 												bool pseudoconstant,
 												Index security_level,
 												Relids required_relids,
@@ -33,7 +32,6 @@ static RestrictInfo *make_restrictinfo_internal(PlannerInfo *root,
 static Expr *make_sub_restrictinfos(PlannerInfo *root,
 									Expr *clause,
 									bool is_pushed_down,
-									bool outerjoin_delayed,
 									bool pseudoconstant,
 									Index security_level,
 									Relids required_relids,
@@ -45,7 +43,7 @@ static Expr *make_sub_restrictinfos(PlannerInfo *root,
  *
  * Build a RestrictInfo node containing the given subexpression.
  *
- * The is_pushed_down, outerjoin_delayed, and pseudoconstant flags for the
+ * The is_pushed_down and pseudoconstant flags for the
  * RestrictInfo must be supplied by the caller, as well as the correct values
  * for security_level and outer_relids.
  * required_relids can be NULL, in which case it defaults to the actual clause
@@ -63,7 +61,6 @@ RestrictInfo *
 make_restrictinfo(PlannerInfo *root,
 				  Expr *clause,
 				  bool is_pushed_down,
-				  bool outerjoin_delayed,
 				  bool pseudoconstant,
 				  Index security_level,
 				  Relids required_relids,
@@ -77,7 +74,6 @@ make_restrictinfo(PlannerInfo *root,
 		return (RestrictInfo *) make_sub_restrictinfos(root,
 													   clause,
 													   is_pushed_down,
-													   outerjoin_delayed,
 													   pseudoconstant,
 													   security_level,
 													   required_relids,
@@ -90,7 +86,6 @@ make_restrictinfo(PlannerInfo *root,
 									  clause,
 									  NULL,
 									  is_pushed_down,
-									  outerjoin_delayed,
 									  pseudoconstant,
 									  security_level,
 									  required_relids,
@@ -107,7 +102,6 @@ make_restrictinfo_internal(PlannerInfo *root,
 						   Expr *clause,
 						   Expr *orclause,
 						   bool is_pushed_down,
-						   bool outerjoin_delayed,
 						   bool pseudoconstant,
 						   Index security_level,
 						   Relids required_relids,
@@ -119,7 +113,6 @@ make_restrictinfo_internal(PlannerInfo *root,
 	restrictinfo->clause = clause;
 	restrictinfo->orclause = orclause;
 	restrictinfo->is_pushed_down = is_pushed_down;
-	restrictinfo->outerjoin_delayed = outerjoin_delayed;
 	restrictinfo->pseudoconstant = pseudoconstant;
 	restrictinfo->has_clone = false;	/* may get set by caller */
 	restrictinfo->is_clone = false; /* may get set by caller */
@@ -251,7 +244,7 @@ make_restrictinfo_internal(PlannerInfo *root,
  * implicit-AND lists at top level of RestrictInfo lists.  Only ORs and
  * simple clauses are valid RestrictInfos.
  *
- * The same is_pushed_down, outerjoin_delayed, and pseudoconstant flag
+ * The same is_pushed_down and pseudoconstant flag
  * values can be applied to all RestrictInfo nodes in the result.  Likewise
  * for security_level and outer_relids.
  *
@@ -263,7 +256,6 @@ static Expr *
 make_sub_restrictinfos(PlannerInfo *root,
 					   Expr *clause,
 					   bool is_pushed_down,
-					   bool outerjoin_delayed,
 					   bool pseudoconstant,
 					   Index security_level,
 					   Relids required_relids,
@@ -279,7 +271,6 @@ make_sub_restrictinfos(PlannerInfo *root,
 							 make_sub_restrictinfos(root,
 													lfirst(temp),
 													is_pushed_down,
-													outerjoin_delayed,
 													pseudoconstant,
 													security_level,
 													NULL,
@@ -288,7 +279,6 @@ make_sub_restrictinfos(PlannerInfo *root,
 												   clause,
 												   make_orclause(orlist),
 												   is_pushed_down,
-												   outerjoin_delayed,
 												   pseudoconstant,
 												   security_level,
 												   required_relids,
@@ -304,7 +294,6 @@ make_sub_restrictinfos(PlannerInfo *root,
 							  make_sub_restrictinfos(root,
 													 lfirst(temp),
 													 is_pushed_down,
-													 outerjoin_delayed,
 													 pseudoconstant,
 													 security_level,
 													 required_relids,
@@ -316,7 +305,6 @@ make_sub_restrictinfos(PlannerInfo *root,
 												   clause,
 												   NULL,
 												   is_pushed_down,
-												   outerjoin_delayed,
 												   pseudoconstant,
 												   security_level,
 												   required_relids,
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index 56df0e92eb..f843659a18 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -2398,24 +2398,12 @@ typedef struct LimitPath
  * conditions.  Possibly we should rename it to reflect that meaning?  But
  * see also the comments for RINFO_IS_PUSHED_DOWN, below.)
  *
- * RestrictInfo nodes also contain an outerjoin_delayed flag, which is true
- * if the clause's applicability must be delayed due to any outer joins
- * appearing below it (ie, it has to be postponed to some join level higher
- * than the set of relations it actually references).
- *
  * There is also an outer_relids field, which is NULL except for outer join
  * clauses; for those, it is the set of relids on the outer side of the
  * clause's outer join.  (These are rels that the clause cannot be applied to
  * in parameterized scans, since pushing it into the join's outer side would
  * lead to wrong answers.)
  *
- * XXX this comment needs work, if we don't remove it completely:
- * outerjoin_delayed = true is subtly different from nullable_relids != NULL:
- * a clause might reference some nullable rels and yet not be
- * outerjoin_delayed because it also references all the other rels of the
- * outer join(s). A clause that is not outerjoin_delayed can be enforced
- * anywhere it is computable.
- *
  * To handle security-barrier conditions efficiently, we mark RestrictInfo
  * nodes with a security_level field, in which higher values identify clauses
  * coming from less-trusted sources.  The exact semantics are that a clause
@@ -2489,9 +2477,6 @@ typedef struct RestrictInfo
 	/* true if clause was pushed down in level */
 	bool		is_pushed_down;
 
-	/* true if delayed by lower outer join */
-	bool		outerjoin_delayed;
-
 	/* see comment above */
 	bool		can_join pg_node_attr(equal_ignore);
 
diff --git a/src/include/optimizer/placeholder.h b/src/include/optimizer/placeholder.h
index 31e1578e82..acb9cf9f05 100644
--- a/src/include/optimizer/placeholder.h
+++ b/src/include/optimizer/placeholder.h
@@ -22,8 +22,6 @@ extern PlaceHolderVar *make_placeholder_expr(PlannerInfo *root, Expr *expr,
 extern PlaceHolderInfo *find_placeholder_info(PlannerInfo *root,
 											  PlaceHolderVar *phv);
 extern void find_placeholders_in_jointree(PlannerInfo *root);
-extern void update_placeholder_eval_levels(PlannerInfo *root,
-										   SpecialJoinInfo *new_sjinfo);
 extern void fix_placeholder_input_needed_levels(PlannerInfo *root);
 extern void add_placeholders_to_base_rels(PlannerInfo *root);
 extern void add_placeholders_to_joinrel(PlannerInfo *root, RelOptInfo *joinrel,
diff --git a/src/include/optimizer/restrictinfo.h b/src/include/optimizer/restrictinfo.h
index f17c341c4b..c9e30776c5 100644
--- a/src/include/optimizer/restrictinfo.h
+++ b/src/include/optimizer/restrictinfo.h
@@ -19,12 +19,11 @@
 
 /* Convenience macro for the common case of a valid-everywhere qual */
 #define make_simple_restrictinfo(root, clause)  \
-	make_restrictinfo(root, clause, true, false, false, 0, NULL, NULL)
+	make_restrictinfo(root, clause, true, false, 0, NULL, NULL)
 
 extern RestrictInfo *make_restrictinfo(PlannerInfo *root,
 									   Expr *clause,
 									   bool is_pushed_down,
-									   bool outerjoin_delayed,
 									   bool pseudoconstant,
 									   Index security_level,
 									   Relids required_relids,
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index d2874c1cad..806732cee9 100644
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -4020,10 +4020,10 @@ explain (costs off)
 select q1, unique2, thousand, hundred
   from int8_tbl a left join tenk1 b on q1 = unique2
   where coalesce(thousand,123) = q1 and q1 = coalesce(hundred,123);
-                                      QUERY PLAN                                      
---------------------------------------------------------------------------------------
+                                                QUERY PLAN                                                
+----------------------------------------------------------------------------------------------------------
  Nested Loop Left Join
-   Filter: ((COALESCE(b.thousand, 123) = a.q1) AND (a.q1 = COALESCE(b.hundred, 123)))
+   Filter: ((COALESCE(b.thousand, 123) = COALESCE(b.hundred, 123)) AND (a.q1 = COALESCE(b.hundred, 123)))
    ->  Seq Scan on int8_tbl a
    ->  Index Scan using tenk1_unique2 on tenk1 b
          Index Cond: (unique2 = a.q1)
commit 40210d3392166d1e277e1948db56829ce38ad1bd
Author: Tom Lane <[email-masked]>
Date:   Mon Jan 23 15:28:34 2023 -0500

    Invent "join domains" to replace the below_outer_join hack.
    
    EquivalenceClasses are now understood as applying within a "join
    domain", which is a set of inner-joined relations (possibly underneath
    an outer join).  We no longer need to treat an EC from below an outer
    join as a second-class citizen.
    
    I have hopes of eventually being able to treat outer-join clauses via
    EquivalenceClasses, by means of only applying deductions within the
    EC's join domain.  There are still problems in the way of that, though,
    so for now the reconsider_outer_join_clause logic is still here.
    
    I haven't been able to get rid of is_pushed_down either, but I wonder
    if that could be recast using JoinDomains.
    
    I had to hack one test case in postgres_fdw.sql to make it still test
    what it was meant to, because postgres_fdw is inconsistent about
    how it deals with quals containing non-shippable expressions; see
    https://postgr.es/m/[email-masked].  That should
    be improved, but I don't think it's within the scope of this patch
    series.

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2350cfe148..d5fc61446a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2513,7 +2513,7 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.*, COALESCE(ft1.c3 || ft2.c3, 'foo
 ALTER SERVER loopback OPTIONS (DROP extensions);
 ALTER SERVER loopback OPTIONS (ADD fdw_startup_cost '10000.0');
 EXPLAIN (VERBOSE, COSTS OFF)
-SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND ft1.c1 = postgres_fdw_abs(ft2.c2))) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
+SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND (ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
                                                                                                                                                                                                                             QUERY PLAN                                                                                                                                                                                                                             
 -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  LockRows
@@ -2527,7 +2527,7 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.
                Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*
                ->  Foreign Scan
                      Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*
-                     Filter: (ft1.c1 = postgres_fdw_abs(ft2.c2))
+                     Filter: ((ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)
                      Relations: (public.ft1) INNER JOIN (public.ft2)
                      Remote SQL: SELECT r4."C 1", r4.c2, r4.c3, r4.c4, r4.c5, r4.c6, r4.c7, r4.c8, CASE WHEN (r4.*)::text IS NOT NULL THEN ROW(r4."C 1", r4.c2, r4.c3, r4.c4, r4.c5, r4.c6, r4.c7, r4.c8) END, CASE WHEN (r5.*)::text IS NOT NULL THEN ROW(r5."C 1", r5.c2, r5.c3, r5.c4, r5.c5, r5.c6, r5.c7, r5.c8) END, r5.c2 FROM ("S 1"."T 1" r4 INNER JOIN "S 1"."T 1" r5 ON (((r5."C 1" = r4."C 1")) AND ((r4."C 1" < 100)))) ORDER BY r4.c3 ASC NULLS LAST
                      ->  Sort
@@ -2535,18 +2535,18 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.
                            Sort Key: ft1.c3
                            ->  Merge Join
                                  Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*, ft2.*, ft2.c2
-                                 Merge Cond: ((ft1.c1 = (postgres_fdw_abs(ft2.c2))) AND (ft1.c1 = ft2.c1))
+                                 Merge Cond: (ft1.c1 = ft2.c1)
+                                 Join Filter: ((ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)
                                  ->  Sort
                                        Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*
                                        Sort Key: ft1.c1
                                        ->  Foreign Scan on public.ft1
                                              Output: ft1.c1, ft1.c2, ft1.c3, ft1.c4, ft1.c5, ft1.c6, ft1.c7, ft1.c8, ft1.*
                                              Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE (("C 1" < 100))
-                                 ->  Sort
-                                       Output: ft2.*, ft2.c1, ft2.c2, (postgres_fdw_abs(ft2.c2))
-                                       Sort Key: (postgres_fdw_abs(ft2.c2)), ft2.c1
+                                 ->  Materialize
+                                       Output: ft2.*, ft2.c1, ft2.c2
                                        ->  Foreign Scan on public.ft2
-                                             Output: ft2.*, ft2.c1, ft2.c2, postgres_fdw_abs(ft2.c2)
+                                             Output: ft2.*, ft2.c1, ft2.c2
                                              Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" ORDER BY "C 1" ASC NULLS LAST
 (32 rows)
 
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index c37aa80383..1e50be137b 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -681,7 +681,7 @@ SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.*, COALESCE(ft1.c3 || ft2.c3, 'foo
 ALTER SERVER loopback OPTIONS (DROP extensions);
 ALTER SERVER loopback OPTIONS (ADD fdw_startup_cost '10000.0');
 EXPLAIN (VERBOSE, COSTS OFF)
-SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND ft1.c1 = postgres_fdw_abs(ft2.c2))) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
+SELECT * FROM local_tbl LEFT JOIN (SELECT ft1.* FROM ft1 INNER JOIN ft2 ON (ft1.c1 = ft2.c1 AND ft1.c1 < 100 AND (ft1.c1 - postgres_fdw_abs(ft2.c2)) = 0)) ss ON (local_tbl.c3 = ss.c3) ORDER BY local_tbl.c1 FOR UPDATE OF local_tbl;
 ALTER SERVER loopback OPTIONS (DROP fdw_startup_cost);
 ALTER SERVER loopback OPTIONS (ADD extensions 'postgres_fdw');
 
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 6b368b08b2..ba00b99249 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -468,7 +468,6 @@ _outEquivalenceClass(StringInfo str, const EquivalenceClass *node)
 	WRITE_BITMAPSET_FIELD(ec_relids);
 	WRITE_BOOL_FIELD(ec_has_const);
 	WRITE_BOOL_FIELD(ec_has_volatile);
-	WRITE_BOOL_FIELD(ec_below_outer_join);
 	WRITE_BOOL_FIELD(ec_broken);
 	WRITE_UINT_FIELD(ec_sortref);
 	WRITE_UINT_FIELD(ec_min_security);
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index fe82b55445..d4b4a4fc7c 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -35,6 +35,7 @@
 
 static EquivalenceMember *add_eq_member(EquivalenceClass *ec,
 										Expr *expr, Relids relids,
+										JoinDomain *jdomain,
 										EquivalenceMember *parent,
 										Oid datatype);
 static bool is_exprlist_member(Expr *node, List *exprs);
@@ -67,6 +68,7 @@ static bool reconsider_outer_join_clause(PlannerInfo *root,
 										 bool outer_on_left);
 static bool reconsider_full_join_clause(PlannerInfo *root,
 										OuterJoinClauseInfo *ojcinfo);
+static JoinDomain *find_join_domain(PlannerInfo *root, Relids relids);
 static Bitmapset *get_eclass_indexes_for_relids(PlannerInfo *root,
 												Relids relids);
 static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
@@ -75,8 +77,8 @@ static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
 
 /*
  * process_equivalence
- *	  The given clause has a mergejoinable operator and can be applied without
- *	  any delay by an outer join, so its two sides can be considered equal
+ *	  The given clause has a mergejoinable operator and is not an outer-join
+ *	  qualification, so its two sides can be considered equal
  *	  anywhere they are both computable; moreover that equality can be
  *	  extended transitively.  Record this knowledge in the EquivalenceClass
  *	  data structure, if applicable.  Returns true if successful, false if not
@@ -88,16 +90,11 @@ static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
  * Then, *p_restrictinfo will be replaced by a new RestrictInfo, which is what
  * the caller should use for further processing.
  *
- * If below_outer_join is true, then the clause was found below the nullable
- * side of an outer join, so its sides might validly be both NULL rather than
- * strictly equal.  We can still deduce equalities in such cases, but we take
- * care to mark an EquivalenceClass if it came from any such clauses.  Also,
- * we have to check that both sides are either pseudo-constants or strict
- * functions of Vars, else they might not both go to NULL above the outer
- * join.  (This is the main reason why we need a failure return.  It's more
- * convenient to check this case here than at the call sites...)
+ * jdomain is the join domain within which the given clause was found.
+ * This limits the applicability of deductions from the EquivalenceClass,
+ * as described in optimizer/README.
  *
- * We also reject proposed equivalence clauses if they contain leaky functions
+ * We reject proposed equivalence clauses if they contain leaky functions
  * and have security_level above zero.  The EC evaluation rules require us to
  * apply certain tests at certain joining levels, and we can't tolerate
  * delaying any test on security_level grounds.  By rejecting candidate clauses
@@ -120,7 +117,7 @@ static Bitmapset *get_common_eclass_indexes(PlannerInfo *root, Relids relids1,
 bool
 process_equivalence(PlannerInfo *root,
 					RestrictInfo **p_restrictinfo,
-					bool below_outer_join)
+					JoinDomain *jdomain)
 {
 	RestrictInfo *restrictinfo = *p_restrictinfo;
 	Expr	   *clause = restrictinfo->clause;
@@ -208,19 +205,6 @@ process_equivalence(PlannerInfo *root,
 		return false;
 	}
 
-	/*
-	 * If below outer join, check for strictness, else reject.
-	 */
-	if (below_outer_join)
-	{
-		if (!bms_is_empty(item1_relids) &&
-			contain_nonstrict_functions((Node *) item1))
-			return false;		/* LHS is non-strict but not constant */
-		if (!bms_is_empty(item2_relids) &&
-			contain_nonstrict_functions((Node *) item2))
-			return false;		/* RHS is non-strict but not constant */
-	}
-
 	/*
 	 * We use the declared input types of the operator, not exprType() of the
 	 * inputs, as the nominal datatypes for opfamily lookup.  This presumes
@@ -285,11 +269,10 @@ process_equivalence(PlannerInfo *root,
 			Assert(!cur_em->em_is_child);	/* no children yet */
 
 			/*
-			 * If below an outer join, don't match constants: they're not as
-			 * constant as they look.
+			 * Match constants only within the same JoinDomain (see
+			 * optimizer/README).
 			 */
-			if ((below_outer_join || cur_ec->ec_below_outer_join) &&
-				cur_em->em_is_const)
+			if (cur_em->em_is_const && cur_em->em_jdomain != jdomain)
 				continue;
 
 			if (!ec1 &&
@@ -326,7 +309,6 @@ process_equivalence(PlannerInfo *root,
 		if (ec1 == ec2)
 		{
 			ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
-			ec1->ec_below_outer_join |= below_outer_join;
 			ec1->ec_min_security = Min(ec1->ec_min_security,
 									   restrictinfo->security_level);
 			ec1->ec_max_security = Max(ec1->ec_max_security,
@@ -362,7 +344,6 @@ process_equivalence(PlannerInfo *root,
 		ec1->ec_relids = bms_join(ec1->ec_relids, ec2->ec_relids);
 		ec1->ec_has_const |= ec2->ec_has_const;
 		/* can't need to set has_volatile */
-		ec1->ec_below_outer_join |= ec2->ec_below_outer_join;
 		ec1->ec_min_security = Min(ec1->ec_min_security,
 								   ec2->ec_min_security);
 		ec1->ec_max_security = Max(ec1->ec_max_security,
@@ -375,7 +356,6 @@ process_equivalence(PlannerInfo *root,
 		ec2->ec_derives = NIL;
 		ec2->ec_relids = NULL;
 		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
-		ec1->ec_below_outer_join |= below_outer_join;
 		ec1->ec_min_security = Min(ec1->ec_min_security,
 								   restrictinfo->security_level);
 		ec1->ec_max_security = Max(ec1->ec_max_security,
@@ -391,9 +371,8 @@ process_equivalence(PlannerInfo *root,
 	{
 		/* Case 3: add item2 to ec1 */
 		em2 = add_eq_member(ec1, item2, item2_relids,
-							NULL, item2_type);
+							jdomain, NULL, item2_type);
 		ec1->ec_sources = lappend(ec1->ec_sources, restrictinfo);
-		ec1->ec_below_outer_join |= below_outer_join;
 		ec1->ec_min_security = Min(ec1->ec_min_security,
 								   restrictinfo->security_level);
 		ec1->ec_max_security = Max(ec1->ec_max_security,
@@ -409,9 +388,8 @@ process_equivalence(PlannerInfo *root,
 	{
 		/* Case 3: add item1 to ec2 */
 		em1 = add_eq_member(ec2, item1, item1_relids,
-							NULL, item1_type);
+							jdomain, NULL, item1_type);
 		ec2->ec_sources = lappend(ec2->ec_sources, restrictinfo);
-		ec2->ec_below_outer_join |= below_outer_join;
 		ec2->ec_min_security = Min(ec2->ec_min_security,
 								   restrictinfo->security_level);
 		ec2->ec_max_security = Max(ec2->ec_max_security,
@@ -436,16 +414,15 @@ process_equivalence(PlannerInfo *root,
 		ec->ec_relids = NULL;
 		ec->ec_has_const = false;
 		ec->ec_has_volatile = false;
-		ec->ec_below_outer_join = below_outer_join;
 		ec->ec_broken = false;
 		ec->ec_sortref = 0;
 		ec->ec_min_security = restrictinfo->security_level;
 		ec->ec_max_security = restrictinfo->security_level;
 		ec->ec_merged = NULL;
 		em1 = add_eq_member(ec, item1, item1_relids,
-							NULL, item1_type);
+							jdomain, NULL, item1_type);
 		em2 = add_eq_member(ec, item2, item2_relids,
-							NULL, item2_type);
+							jdomain, NULL, item2_type);
 
 		root->eq_classes = lappend(root->eq_classes, ec);
 
@@ -535,7 +512,7 @@ canonicalize_ec_expression(Expr *expr, Oid req_type, Oid req_collation)
  */
 static EquivalenceMember *
 add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
-			  EquivalenceMember *parent, Oid datatype)
+			  JoinDomain *jdomain, EquivalenceMember *parent, Oid datatype)
 {
 	EquivalenceMember *em = makeNode(EquivalenceMember);
 
@@ -544,6 +521,7 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
 	em->em_is_const = false;
 	em->em_is_child = (parent != NULL);
 	em->em_datatype = datatype;
+	em->em_jdomain = jdomain;
 	em->em_parent = parent;
 
 	if (bms_is_empty(relids))
@@ -612,6 +590,7 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 						 Relids rel,
 						 bool create_it)
 {
+	JoinDomain *jdomain;
 	Relids		expr_relids;
 	EquivalenceClass *newec;
 	EquivalenceMember *newem;
@@ -623,6 +602,12 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 	 */
 	expr = canonicalize_ec_expression(expr, opcintype, collation);
 
+	/*
+	 * Since SortGroupClause nodes are top-level expressions (GROUP BY, ORDER
+	 * BY, etc), they can be presumed to belong to the top JoinDomain.
+	 */
+	jdomain = linitial_node(JoinDomain, root->join_domains);
+
 	/*
 	 * Scan through the existing EquivalenceClasses for a match
 	 */
@@ -656,11 +641,10 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 				continue;
 
 			/*
-			 * If below an outer join, don't match constants: they're not as
-			 * constant as they look.
+			 * Match constants only within the same JoinDomain (see
+			 * optimizer/README).
 			 */
-			if (cur_ec->ec_below_outer_join &&
-				cur_em->em_is_const)
+			if (cur_em->em_is_const && cur_em->em_jdomain != jdomain)
 				continue;
 
 			if (opcintype == cur_em->em_datatype &&
@@ -689,7 +673,6 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 	newec->ec_relids = NULL;
 	newec->ec_has_const = false;
 	newec->ec_has_volatile = contain_volatile_functions((Node *) expr);
-	newec->ec_below_outer_join = false;
 	newec->ec_broken = false;
 	newec->ec_sortref = sortref;
 	newec->ec_min_security = UINT_MAX;
@@ -705,7 +688,7 @@ get_eclass_for_sort_expr(PlannerInfo *root,
 	expr_relids = pull_varnos(root, (Node *) expr);
 
 	newem = add_eq_member(newec, copyObject(expr), expr_relids,
-						  NULL, opcintype);
+						  jdomain, NULL, opcintype);
 
 	/*
 	 * add_eq_member doesn't check for volatile functions, set-returning
@@ -1185,11 +1168,16 @@ generate_base_implied_equalities_const(PlannerInfo *root,
 			ec->ec_broken = true;
 			break;
 		}
+
+		/*
+		 * We use the constant's em_jdomain as qualscope, so that if the
+		 * generated clause is variable-free (i.e, both EMs are consts) it
+		 * will be enforced at the join domain level.
+		 */
 		rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
 										 cur_em->em_expr, const_em->em_expr,
-										 bms_copy(ec->ec_relids),
+										 const_em->em_jdomain->jd_relids,
 										 ec->ec_min_security,
-										 ec->ec_below_outer_join,
 										 cur_em->em_is_const);
 
 		/*
@@ -1257,11 +1245,16 @@ generate_base_implied_equalities_no_const(PlannerInfo *root,
 				ec->ec_broken = true;
 				break;
 			}
+
+			/*
+			 * The expressions aren't constants, so the passed qualscope will
+			 * never be used to place the generated clause.  We just need to
+			 * be sure it covers both expressions, so ec_relids will serve.
+			 */
 			rinfo = process_implied_equality(root, eq_op, ec->ec_collation,
 											 prev_em->em_expr, cur_em->em_expr,
-											 bms_copy(ec->ec_relids),
+											 ec->ec_relids,
 											 ec->ec_min_security,
-											 ec->ec_below_outer_join,
 											 false);
 
 			/*
@@ -2074,6 +2067,7 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 							 bool outer_on_left)
 {
 	RestrictInfo *rinfo = ojcinfo->rinfo;
+	SpecialJoinInfo *sjinfo = ojcinfo->sjinfo;
 	Expr	   *outervar,
 			   *innervar;
 	Oid			opno,
@@ -2150,6 +2144,7 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
 			Oid			eq_op;
 			RestrictInfo *newrinfo;
+			JoinDomain *jdomain;
 
 			if (!cur_em->em_is_const)
 				continue;		/* ignore non-const members */
@@ -2165,7 +2160,9 @@ reconsider_outer_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo,
 												   cur_em->em_expr,
 												   bms_copy(inner_relids),
 												   cur_ec->ec_min_security);
-			if (process_equivalence(root, &newrinfo, true))
+			/* This equality holds within the OJ's child JoinDomain */
+			jdomain = find_join_domain(root, sjinfo->syn_righthand);
+			if (process_equivalence(root, &newrinfo, jdomain))
 				match = true;
 		}
 
@@ -2300,6 +2297,7 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 			EquivalenceMember *cur_em = (EquivalenceMember *) lfirst(lc2);
 			Oid			eq_op;
 			RestrictInfo *newrinfo;
+			JoinDomain *jdomain;
 
 			if (!cur_em->em_is_const)
 				continue;		/* ignore non-const members */
@@ -2315,7 +2313,9 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 													   cur_em->em_expr,
 													   bms_copy(left_relids),
 													   cur_ec->ec_min_security);
-				if (process_equivalence(root, &newrinfo, true))
+				/* This equality holds within the lefthand child JoinDomain */
+				jdomain = find_join_domain(root, sjinfo->syn_lefthand);
+				if (process_equivalence(root, &newrinfo, jdomain))
 					matchleft = true;
 			}
 			eq_op = select_equality_operator(cur_ec,
@@ -2330,7 +2330,9 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 													   cur_em->em_expr,
 													   bms_copy(right_relids),
 													   cur_ec->ec_min_security);
-				if (process_equivalence(root, &newrinfo, true))
+				/* This equality holds within the righthand child JoinDomain */
+				jdomain = find_join_domain(root, sjinfo->syn_righthand);
+				if (process_equivalence(root, &newrinfo, jdomain))
 					matchright = true;
 			}
 		}
@@ -2359,6 +2361,29 @@ reconsider_full_join_clause(PlannerInfo *root, OuterJoinClauseInfo *ojcinfo)
 	return false;				/* failed to make any deduction */
 }
 
+/*
+ * find_join_domain
+ *	  Find the highest JoinDomain enclosed within the given relid set.
+ *
+ * (We could avoid this search at the cost of complicating APIs elsewhere,
+ * which doesn't seem worth it.)
+ */
+static JoinDomain *
+find_join_domain(PlannerInfo *root, Relids relids)
+{
+	ListCell   *lc;
+
+	foreach(lc, root->join_domains)
+	{
+		JoinDomain *jdomain = (JoinDomain *) lfirst(lc);
+
+		if (bms_is_subset(jdomain->jd_relids, relids))
+			return jdomain;
+	}
+	elog(ERROR, "failed to find appropriate JoinDomain");
+	return NULL;				/* keep compiler quiet */
+}
+
 
 /*
  * exprs_known_equal
@@ -2648,6 +2673,7 @@ add_child_rel_equivalences(PlannerInfo *root,
 				new_relids = bms_add_members(new_relids, child_relids);
 
 				(void) add_eq_member(cur_ec, child_expr, new_relids,
+									 cur_em->em_jdomain,
 									 cur_em, cur_em->em_datatype);
 
 				/* Record this EC index for the child rel */
@@ -2775,6 +2801,7 @@ add_child_join_rel_equivalences(PlannerInfo *root,
 				new_relids = bms_add_members(new_relids, child_relids);
 
 				(void) add_eq_member(cur_ec, child_expr, new_relids,
+									 cur_em->em_jdomain,
 									 cur_em, cur_em->em_datatype);
 			}
 		}
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 7591a7d81d..e69dc31237 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -2321,18 +2321,6 @@ select_mergejoin_clauses(PlannerInfo *root,
 		 * canonical pathkey list, but redundant eclasses can't appear in
 		 * canonical sort orderings.  (XXX it might be worth relaxing this,
 		 * but not enough time to address it for 8.3.)
-		 *
-		 * Note: it would be bad if this condition failed for an otherwise
-		 * mergejoinable FULL JOIN clause, since that would result in
-		 * undesirable planner failure.  I believe that is not possible
-		 * however; a variable involved in a full join could only appear in
-		 * below_outer_join eclasses, which aren't considered redundant.
-		 *
-		 * This case *can* happen for left/right join clauses: the outer-side
-		 * variable could be equated to a constant.  Because we will propagate
-		 * that constant across the join clause, the loss of ability to do a
-		 * mergejoin is not really all that big a deal, and so it's not clear
-		 * that improving this is important.
 		 */
 		update_mergeclause_eclasses(root, restrictinfo);
 
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 4c99b28d0a..1b11852814 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -6210,10 +6210,7 @@ prepare_sort_from_pathkeys(Plan *lefttree, List *pathkeys,
 			 * the pathkey's EquivalenceClass.  For now, we take the first
 			 * tlist item found in the EC. If there's no match, we'll generate
 			 * a resjunk entry using the first EC member that is an expression
-			 * in the input's vars.  (The non-const restriction only matters
-			 * if the EC is below_outer_join; but if it isn't, it won't
-			 * contain consts anyway, else we'd have discarded the pathkey as
-			 * redundant.)
+			 * in the input's vars.
 			 *
 			 * XXX if we have a choice, is there any way of figuring out which
 			 * might be cheapest to execute?  (For example, int4lt is likely
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 0f4163bffd..35b2dc1034 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -61,7 +61,7 @@ typedef struct JoinTreeItem
 {
 	/* Fields filled during deconstruct_recurse: */
 	Node	   *jtnode;			/* jointree node to examine */
-	bool		below_outer_join;	/* is it below an outer join? */
+	JoinDomain *jdomain;		/* join domain for its ON/WHERE clauses */
 	Relids		qualscope;		/* base+OJ Relids syntactically included in
 								 * this jointree node */
 	Relids		inner_join_rels;	/* base+OJ Relids syntactically included
@@ -87,13 +87,13 @@ typedef struct PostponedQual
 static void extract_lateral_references(PlannerInfo *root, RelOptInfo *brel,
 									   Index rtindex);
 static List *deconstruct_recurse(PlannerInfo *root, Node *jtnode,
-								 bool below_outer_join,
+								 JoinDomain *parent_domain,
 								 List **item_list);
 static void deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 								   List **postponed_qual_list);
 static void process_security_barrier_quals(PlannerInfo *root,
 										   int rti, Relids qualscope,
-										   bool below_outer_join);
+										   JoinDomain *jdomain);
 static void mark_rels_nulled_by_join(PlannerInfo *root, Index ojrelid,
 									 Relids lower_rels);
 static SpecialJoinInfo *make_outerjoininfo(PlannerInfo *root,
@@ -107,7 +107,7 @@ static void deconstruct_distribute_oj_quals(PlannerInfo *root,
 											List *jtitems,
 											JoinTreeItem *jtitem);
 static void distribute_quals_to_rels(PlannerInfo *root, List *clauses,
-									 bool below_outer_join,
+									 JoinDomain *jdomain,
 									 SpecialJoinInfo *sjinfo,
 									 Index security_level,
 									 Relids qualscope,
@@ -119,7 +119,7 @@ static void distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 									 List **postponed_qual_list,
 									 List **postponed_oj_qual_list);
 static void distribute_qual_to_rels(PlannerInfo *root, Node *clause,
-									bool below_outer_join,
+									JoinDomain *jdomain,
 									SpecialJoinInfo *sjinfo,
 									Index security_level,
 									Relids qualscope,
@@ -740,6 +740,7 @@ List *
 deconstruct_jointree(PlannerInfo *root)
 {
 	List	   *result;
+	JoinDomain *top_jdomain;
 	List	   *item_list = NIL;
 	List	   *postponed_qual_list = NIL;
 	ListCell   *lc;
@@ -751,6 +752,10 @@ deconstruct_jointree(PlannerInfo *root)
 	 */
 	root->placeholdersFrozen = true;
 
+	/* Fetch the already-created top-level join domain for the query */
+	top_jdomain = linitial_node(JoinDomain, root->join_domains);
+	top_jdomain->jd_relids = NULL;	/* filled during deconstruct_recurse */
+
 	/* Start recursion at top of jointree */
 	Assert(root->parse->jointree != NULL &&
 		   IsA(root->parse->jointree, FromExpr));
@@ -761,12 +766,15 @@ deconstruct_jointree(PlannerInfo *root)
 
 	/* Perform the initial scan of the jointree */
 	result = deconstruct_recurse(root, (Node *) root->parse->jointree,
-								 false,
+								 top_jdomain,
 								 &item_list);
 
 	/* Now we can form the value of all_query_rels, too */
 	root->all_query_rels = bms_union(root->all_baserels, root->outer_join_rels);
 
+	/* ... which should match what we computed for the top join domain */
+	Assert(bms_equal(root->all_query_rels, top_jdomain->jd_relids));
+
 	/* Now scan all the jointree nodes again, and distribute quals */
 	foreach(lc, item_list)
 	{
@@ -804,10 +812,9 @@ deconstruct_jointree(PlannerInfo *root)
  * deconstruct_recurse
  *	  One recursion level of deconstruct_jointree's initial jointree scan.
  *
- * Inputs:
- *	jtnode is the jointree node to examine
- *	below_outer_join is true if this node is within the nullable side of a
- *		higher-level outer join
+ * jtnode is the jointree node to examine, and parent_domain is the
+ * enclosing join domain.  (We must add all base+OJ relids appearing
+ * here or below to parent_domain.)
  *
  * item_list is an in/out parameter: we add a JoinTreeItem struct to
  * that list for each jointree node, in depth-first traversal order.
@@ -817,7 +824,7 @@ deconstruct_jointree(PlannerInfo *root)
  */
 static List *
 deconstruct_recurse(PlannerInfo *root, Node *jtnode,
-					bool below_outer_join,
+					JoinDomain *parent_domain,
 					List **item_list)
 {
 	List	   *joinlist;
@@ -828,7 +835,6 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 	/* Make the new JoinTreeItem, but don't add it to item_list yet */
 	jtitem = palloc0_object(JoinTreeItem);
 	jtitem->jtnode = jtnode;
-	jtitem->below_outer_join = below_outer_join;
 
 	if (IsA(jtnode, RangeTblRef))
 	{
@@ -836,6 +842,10 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 
 		/* Fill all_baserels as we encounter baserel jointree nodes */
 		root->all_baserels = bms_add_member(root->all_baserels, varno);
+		/* This node belongs to parent_domain */
+		jtitem->jdomain = parent_domain;
+		parent_domain->jd_relids = bms_add_member(parent_domain->jd_relids,
+												  varno);
 		/* qualscope is just the one RTE */
 		jtitem->qualscope = bms_make_singleton(varno);
 		/* A single baserel does not create an inner join */
@@ -848,6 +858,9 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 		int			remaining;
 		ListCell   *l;
 
+		/* This node belongs to parent_domain, as do its children */
+		jtitem->jdomain = parent_domain;
+
 		/*
 		 * Recurse to handle child nodes, and compute output joinlist.  We
 		 * collapse subproblems into a single joinlist whenever the resulting
@@ -866,7 +879,7 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 			int			sub_members;
 
 			sub_joinlist = deconstruct_recurse(root, lfirst(l),
-											   below_outer_join,
+											   parent_domain,
 											   item_list);
 			sub_item = (JoinTreeItem *) llast(*item_list);
 			jtitem->qualscope = bms_add_members(jtitem->qualscope,
@@ -894,6 +907,8 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 	else if (IsA(jtnode, JoinExpr))
 	{
 		JoinExpr   *j = (JoinExpr *) jtnode;
+		JoinDomain *child_domain,
+				   *fj_domain;
 		JoinTreeItem *left_item,
 				   *right_item;
 		List	   *leftjoinlist,
@@ -902,13 +917,15 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 		switch (j->jointype)
 		{
 			case JOIN_INNER:
+				/* This node belongs to parent_domain, as do its children */
+				jtitem->jdomain = parent_domain;
 				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
-												   below_outer_join,
+												   parent_domain,
 												   item_list);
 				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
-													below_outer_join,
+													parent_domain,
 													item_list);
 				right_item = (JoinTreeItem *) llast(*item_list);
 				/* Compute qualscope etc */
@@ -922,21 +939,32 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				break;
 			case JOIN_LEFT:
 			case JOIN_ANTI:
+				/* Make new join domain for my quals and the RHS */
+				child_domain = makeNode(JoinDomain);
+				child_domain->jd_relids = NULL; /* filled by recursion */
+				root->join_domains = lappend(root->join_domains, child_domain);
+				jtitem->jdomain = child_domain;
 				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
-												   below_outer_join,
+												   parent_domain,
 												   item_list);
 				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
-													true,
+													child_domain,
 													item_list);
 				right_item = (JoinTreeItem *) llast(*item_list);
-				/* Compute qualscope etc */
+				/* Compute join domain contents, qualscope etc */
+				parent_domain->jd_relids =
+					bms_add_members(parent_domain->jd_relids,
+									child_domain->jd_relids);
 				jtitem->qualscope = bms_union(left_item->qualscope,
 											  right_item->qualscope);
 				/* caution: ANTI join derived from SEMI will lack rtindex */
 				if (j->rtindex != 0)
 				{
+					parent_domain->jd_relids =
+						bms_add_member(parent_domain->jd_relids,
+									   j->rtindex);
 					jtitem->qualscope = bms_add_member(jtitem->qualscope,
 													   j->rtindex);
 					root->outer_join_rels = bms_add_member(root->outer_join_rels,
@@ -951,13 +979,15 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->nonnullable_rels = left_item->qualscope;
 				break;
 			case JOIN_SEMI:
+				/* This node belongs to parent_domain, as do its children */
+				jtitem->jdomain = parent_domain;
 				/* Recurse */
 				leftjoinlist = deconstruct_recurse(root, j->larg,
-												   below_outer_join,
+												   parent_domain,
 												   item_list);
 				left_item = (JoinTreeItem *) llast(*item_list);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
-													below_outer_join,
+													parent_domain,
 													item_list);
 				right_item = (JoinTreeItem *) llast(*item_list);
 				/* Compute qualscope etc */
@@ -973,19 +1003,36 @@ deconstruct_recurse(PlannerInfo *root, Node *jtnode,
 				jtitem->nonnullable_rels = NULL;
 				break;
 			case JOIN_FULL:
-				/* Recurse */
+				/* The FULL JOIN's quals need their very own domain */
+				fj_domain = makeNode(JoinDomain);
+				root->join_domains = lappend(root->join_domains, fj_domain);
+				jtitem->jdomain = fj_domain;
+				/* Recurse, giving each side its own join domain */
+				child_domain = makeNode(JoinDomain);
+				child_domain->jd_relids = NULL; /* filled by recursion */
+				root->join_domains = lappend(root->join_domains, child_domain);
 				leftjoinlist = deconstruct_recurse(root, j->larg,
-												   true,
+												   child_domain,
 												   item_list);
 				left_item = (JoinTreeItem *) llast(*item_list);
+				fj_domain->jd_relids = bms_copy(child_domain->jd_relids);
+				child_domain = makeNode(JoinDomain);
+				child_domain->jd_relids = NULL; /* filled by recursion */
+				root->join_domains = lappend(root->join_domains, child_domain);
 				rightjoinlist = deconstruct_recurse(root, j->rarg,
-													true,
+													child_domain,
 													item_list);
 				right_item = (JoinTreeItem *) llast(*item_list);
 				/* Compute qualscope etc */
+				fj_domain->jd_relids = bms_add_members(fj_domain->jd_relids,
+													   child_domain->jd_relids);
+				parent_domain->jd_relids = bms_add_members(parent_domain->jd_relids,
+														   fj_domain->jd_relids);
 				jtitem->qualscope = bms_union(left_item->qualscope,
 											  right_item->qualscope);
 				Assert(j->rtindex != 0);
+				parent_domain->jd_relids = bms_add_member(parent_domain->jd_relids,
+														  j->rtindex);
 				jtitem->qualscope = bms_add_member(jtitem->qualscope,
 												   j->rtindex);
 				root->outer_join_rels = bms_add_member(root->outer_join_rels,
@@ -1087,7 +1134,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 			process_security_barrier_quals(root,
 										   varno,
 										   jtitem->qualscope,
-										   jtitem->below_outer_join);
+										   jtitem->jdomain);
 	}
 	else if (IsA(jtnode, FromExpr))
 	{
@@ -1105,7 +1152,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 
 			if (bms_is_subset(pq->relids, jtitem->qualscope))
 				distribute_qual_to_rels(root, pq->qual,
-										jtitem->below_outer_join,
+										jtitem->jdomain,
 										NULL,
 										root->qual_security_level,
 										jtitem->qualscope, NULL, NULL,
@@ -1120,7 +1167,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 		 * Now process the top-level quals.
 		 */
 		distribute_quals_to_rels(root, (List *) f->quals,
-								 jtitem->below_outer_join,
+								 jtitem->jdomain,
 								 NULL,
 								 root->qual_security_level,
 								 jtitem->qualscope, NULL, NULL,
@@ -1221,7 +1268,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 
 		/* Process the JOIN's qual clauses */
 		distribute_quals_to_rels(root, my_quals,
-								 jtitem->below_outer_join,
+								 jtitem->jdomain,
 								 sjinfo,
 								 root->qual_security_level,
 								 jtitem->qualscope,
@@ -1258,7 +1305,7 @@ deconstruct_distribute(PlannerInfo *root, JoinTreeItem *jtitem,
 static void
 process_security_barrier_quals(PlannerInfo *root,
 							   int rti, Relids qualscope,
-							   bool below_outer_join)
+							   JoinDomain *jdomain)
 {
 	RangeTblEntry *rte = root->simple_rte_array[rti];
 	Index		security_level = 0;
@@ -1281,7 +1328,7 @@ process_security_barrier_quals(PlannerInfo *root,
 		 * pushed up to top of tree, which we don't want.
 		 */
 		distribute_quals_to_rels(root, qualset,
-								 below_outer_join,
+								 jdomain,
 								 NULL,
 								 security_level,
 								 qualscope,
@@ -1991,7 +2038,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
 			is_clone = !has_clone;
 
 			distribute_quals_to_rels(root, quals,
-									 true,
+									 otherjtitem->jdomain,
 									 sjinfo,
 									 root->qual_security_level,
 									 this_qualscope,
@@ -2020,7 +2067,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
 	{
 		/* No commutation possible, just process the postponed clauses */
 		distribute_quals_to_rels(root, jtitem->oj_joinclauses,
-								 true,
+								 jtitem->jdomain,
 								 sjinfo,
 								 root->qual_security_level,
 								 qualscope,
@@ -2045,7 +2092,7 @@ deconstruct_distribute_oj_quals(PlannerInfo *root,
  */
 static void
 distribute_quals_to_rels(PlannerInfo *root, List *clauses,
-						 bool below_outer_join,
+						 JoinDomain *jdomain,
 						 SpecialJoinInfo *sjinfo,
 						 Index security_level,
 						 Relids qualscope,
@@ -2064,7 +2111,7 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
 		Node	   *clause = (Node *) lfirst(lc);
 
 		distribute_qual_to_rels(root, clause,
-								below_outer_join,
+								jdomain,
 								sjinfo,
 								security_level,
 								qualscope,
@@ -2092,8 +2139,7 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
  * These will be dealt with in later steps of deconstruct_jointree.
  *
  * 'clause': the qual clause to be distributed
- * 'below_outer_join': true if the qual is from a JOIN/ON that is below the
- *		nullable side of a higher-level outer join
+ * 'jdomain': the join domain containing the clause
  * 'sjinfo': join's SpecialJoinInfo (NULL for an inner join or WHERE clause)
  * 'security_level': security_level to assign to the qual
  * 'qualscope': set of base+OJ rels the qual's syntactic scope covers
@@ -2124,7 +2170,7 @@ distribute_quals_to_rels(PlannerInfo *root, List *clauses,
  */
 static void
 distribute_qual_to_rels(PlannerInfo *root, Node *clause,
-						bool below_outer_join,
+						JoinDomain *jdomain,
 						SpecialJoinInfo *sjinfo,
 						Index security_level,
 						Relids qualscope,
@@ -2196,12 +2242,8 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	 * RestrictInfo lists for the moment, but eventually createplan.c will
 	 * pull it out and make a gating Result node immediately above whatever
 	 * plan node the pseudoconstant clause is assigned to.  It's usually best
-	 * to put a gating node as high in the plan tree as possible. If we are
-	 * not below an outer join, we can actually push the pseudoconstant qual
-	 * all the way to the top of the tree.  If we are below an outer join, we
-	 * leave the qual at its original syntactic level (we could push it up to
-	 * just below the outer join, but that seems more complex than it's
-	 * worth).
+	 * to put a gating node as high in the plan tree as possible, which we can
+	 * do by assigning it the full relid set of the current JoinDomain.
 	 */
 	if (bms_is_empty(relids))
 	{
@@ -2211,25 +2253,20 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 			relids = bms_copy(ojscope);
 			/* mustn't use as gating qual, so don't mark pseudoconstant */
 		}
-		else
+		else if (contain_volatile_functions(clause))
 		{
 			/* eval at original syntactic level */
 			relids = bms_copy(qualscope);
-			if (!contain_volatile_functions(clause))
-			{
-				/* mark as gating qual */
-				pseudoconstant = true;
-				/* tell createplan.c to check for gating quals */
-				root->hasPseudoConstantQuals = true;
-				/* if not below outer join, push it to top of tree */
-				if (!below_outer_join)
-				{
-					relids =
-						get_relids_in_jointree((Node *) root->parse->jointree,
-											   true, false);
-					qualscope = bms_copy(relids);
-				}
-			}
+			/* again, can't mark pseudoconstant */
+		}
+		else
+		{
+			/* eval at join domain level */
+			relids = bms_copy(jdomain->jd_relids);
+			/* mark as gating qual */
+			pseudoconstant = true;
+			/* tell createplan.c to check for gating quals */
+			root->hasPseudoConstantQuals = true;
 		}
 	}
 
@@ -2319,23 +2356,8 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 		if (check_redundant_nullability_qual(root, clause))
 			return;
 
-		if (!allow_equivalence)
-		{
-			/* Caller says it mustn't become an equivalence class */
-			maybe_equivalence = false;
-		}
-		else
-		{
-			/*
-			 * Consider feeding qual to the equivalence machinery.  However,
-			 * if it's itself within an outer-join clause, treat it as though
-			 * it appeared below that outer join (note that we can only get
-			 * here when the clause references only nullable-side rels).
-			 */
-			maybe_equivalence = true;
-			if (outerjoin_nonnullable != NULL)
-				below_outer_join = true;
-		}
+		/* Feed qual to the equivalence machinery, if allowed by caller */
+		maybe_equivalence = allow_equivalence;
 
 		/*
 		 * Since it doesn't mention the LHS, it's certainly not useful as a
@@ -2401,16 +2423,14 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	check_mergejoinable(restrictinfo);
 
 	/*
-	 * XXX rewrite:
-	 *
 	 * If it is a true equivalence clause, send it to the EquivalenceClass
 	 * machinery.  We do *not* attach it directly to any restriction or join
 	 * lists.  The EC code will propagate it to the appropriate places later.
 	 *
-	 * If the clause has a mergejoinable operator and is not
-	 * outerjoin-delayed, yet isn't an equivalence because it is an outer-join
-	 * clause, the EC code may yet be able to do something with it.  We add it
-	 * to appropriate lists for further consideration later.  Specifically:
+	 * If the clause has a mergejoinable operator, yet isn't an equivalence
+	 * because it is an outer-join clause, the EC code may still be able to do
+	 * something with it.  We add it to appropriate lists for further
+	 * consideration later.  Specifically:
 	 *
 	 * If it is a left or right outer-join qualification that relates the two
 	 * sides of the outer join (no funny business like leftvar1 = leftvar2 +
@@ -2438,7 +2458,7 @@ distribute_qual_to_rels(PlannerInfo *root, Node *clause,
 	{
 		if (maybe_equivalence)
 		{
-			if (process_equivalence(root, &restrictinfo, below_outer_join))
+			if (process_equivalence(root, &restrictinfo, jdomain))
 				return;
 			/* EC rejected it, so set left_ec/right_ec the hard way ... */
 			if (restrictinfo->mergeopfamilies)	/* EC might have changed this */
@@ -2628,8 +2648,9 @@ distribute_restrictinfo_to_rels(PlannerInfo *root,
  * "qualscope" is the nominal syntactic level to impute to the restrictinfo.
  * This must contain at least all the rels used in the expressions, but it
  * is used only to set the qual application level when both exprs are
- * variable-free.  Otherwise the qual is applied at the lowest join level
- * that provides all its variables.
+ * variable-free.  (Hence, it should usually match the join domain in which
+ * the clause applies.)  Otherwise the qual is applied at the lowest join
+ * level that provides all its variables.
  *
  * "security_level" is the security level to assign to the new restrictinfo.
  *
@@ -2657,7 +2678,6 @@ process_implied_equality(PlannerInfo *root,
 						 Expr *item2,
 						 Relids qualscope,
 						 Index security_level,
-						 bool below_outer_join,
 						 bool both_const)
 {
 	RestrictInfo *restrictinfo;
@@ -2706,27 +2726,16 @@ process_implied_equality(PlannerInfo *root,
 	/*
 	 * If the clause is variable-free, our normal heuristic for pushing it
 	 * down to just the mentioned rels doesn't work, because there are none.
-	 * Apply at the given qualscope, or at the top of tree if it's nonvolatile
-	 * (which it very likely is, but we'll check, just to be sure).
+	 * Apply it as a gating qual at the given qualscope.
 	 */
 	if (bms_is_empty(relids))
 	{
-		/* eval at original syntactic level */
+		/* eval at join domain level */
 		relids = bms_copy(qualscope);
-		if (!contain_volatile_functions(clause))
-		{
-			/* mark as gating qual */
-			pseudoconstant = true;
-			/* tell createplan.c to check for gating quals */
-			root->hasPseudoConstantQuals = true;
-			/* if not below outer join, push it to top of tree */
-			if (!below_outer_join)
-			{
-				relids =
-					get_relids_in_jointree((Node *) root->parse->jointree,
-										   true, false);
-			}
-		}
+		/* mark as gating qual */
+		pseudoconstant = true;
+		/* tell createplan.c to check for gating quals */
+		root->hasPseudoConstantQuals = true;
 	}
 
 	/*
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 8674ad674d..db5ff6fdca 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -625,6 +625,7 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	root->init_plans = NIL;
 	root->cte_plan_ids = NIL;
 	root->multiexpr_params = NIL;
+	root->join_domains = NIL;
 	root->eq_classes = NIL;
 	root->ec_merging_done = false;
 	root->last_rinfo_serial = 0;
@@ -654,6 +655,13 @@ subquery_planner(PlannerGlobal *glob, Query *parse,
 	root->non_recursive_path = NULL;
 	root->partColsUpdated = false;
 
+	/*
+	 * Create the top-level join domain.  This won't have valid contents until
+	 * deconstruct_jointree fills it in, but the node needs to exist before
+	 * that so we can build EquivalenceClasses referencing it.
+	 */
+	root->join_domains = list_make1(makeNode(JoinDomain));
+
 	/*
 	 * If there is a WITH list, process each WITH query and either convert it
 	 * to RTE_SUBQUERY RTE(s) or build an initplan SubPlan structure for it.
@@ -6534,6 +6542,7 @@ plan_cluster_use_sort(Oid tableOid, Oid indexOid)
 	root->query_level = 1;
 	root->planner_cxt = CurrentMemoryContext;
 	root->wt_param_id = -1;
+	root->join_domains = list_make1(makeNode(JoinDomain));
 
 	/* Build a minimal RTE for the rel */
 	rte = makeNode(RangeTblEntry);
@@ -6655,6 +6664,7 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 	root->query_level = 1;
 	root->planner_cxt = CurrentMemoryContext;
 	root->wt_param_id = -1;
+	root->join_domains = list_make1(makeNode(JoinDomain));
 
 	/*
 	 * Build a minimal RTE.
diff --git a/src/backend/optimizer/prep/prepjointree.c b/src/backend/optimizer/prep/prepjointree.c
index eacfb66b31..870d84b29d 100644
--- a/src/backend/optimizer/prep/prepjointree.c
+++ b/src/backend/optimizer/prep/prepjointree.c
@@ -991,6 +991,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->init_plans = NIL;
 	subroot->cte_plan_ids = NIL;
 	subroot->multiexpr_params = NIL;
+	subroot->join_domains = NIL;
 	subroot->eq_classes = NIL;
 	subroot->ec_merging_done = false;
 	subroot->last_rinfo_serial = 0;
@@ -1012,6 +1013,7 @@ pull_up_simple_subquery(PlannerInfo *root, Node *jtnode, RangeTblEntry *rte,
 	subroot->hasRecursion = false;
 	subroot->wt_param_id = -1;
 	subroot->non_recursive_path = NULL;
+	/* We don't currently need a top JoinDomain for the subroot */
 
 	/* No CTEs to worry about */
 	Assert(subquery->cteList == NIL);
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h
index f843659a18..62d9460258 100644
--- a/src/include/nodes/pathnodes.h
+++ b/src/include/nodes/pathnodes.h
@@ -307,6 +307,9 @@ struct PlannerInfo
 	/* List of Lists of Params for MULTIEXPR subquery outputs */
 	List	   *multiexpr_params;
 
+	/* list of JoinDomains used in the query (higher ones first) */
+	List	   *join_domains;
+
 	/* list of active EquivalenceClasses */
 	List	   *eq_classes;
 
@@ -1278,11 +1281,46 @@ typedef struct StatisticExtInfo
 	List	   *exprs;
 } StatisticExtInfo;
 
+/*
+ * JoinDomains
+ *
+ * A "join domain" defines the scope of applicability of deductions made via
+ * the EquivalenceClass mechanism.  Roughly speaking, a join domain is a set
+ * of base+OJ relations that are inner-joined together.  More precisely, it is
+ * the set of relations at which equalities deduced from an EquivalenceClass
+ * can be enforced or should be expected to hold.  The topmost JoinDomain
+ * covers the whole query (so its jd_relids should equal all_query_rels).
+ * An outer join creates a new JoinDomain that includes all base+OJ relids
+ * within its nullable side, but (by convention) not the OJ's own relid.
+ * A FULL join creates two new JoinDomains, one for each side.
+ *
+ * Notice that a rel that is below outer join(s) will thus appear to belong
+ * to multiple join domains.  However, any of its Vars that appear in
+ * EquivalenceClasses belonging to higher join domains will have nullingrel
+ * bits preventing them from being evaluated at the rel's scan level, so that
+ * we will not be able to derive enforceable-at-the-rel-scan-level clauses
+ * from such ECs.  We define the join domain relid sets this way so that
+ * domains can be said to be "higher" or "lower" when one domain relid set
+ * includes another.
+ *
+ * The JoinDomains for a query are computed in deconstruct_jointree.
+ * We do not copy JoinDomain structs once made, so they can be compared
+ * for equality by simple pointer equality.
+ */
+typedef struct JoinDomain
+{
+	pg_node_attr(no_copy_equal, no_read)
+
+	NodeTag		type;
+
+	Relids		jd_relids;		/* all relids contained within the domain */
+} JoinDomain;
+
 /*
  * EquivalenceClasses
  *
- * Whenever we can determine that a mergejoinable equality clause A = B is
- * not delayed by any outer join, we create an EquivalenceClass containing
+ * Whenever we identify a mergejoinable equality clause A = B that is
+ * not an outer-join clause, we create an EquivalenceClass containing
  * the expressions A and B to record this knowledge.  If we later find another
  * equivalence B = C, we add C to the existing EquivalenceClass; this may
  * require merging two existing EquivalenceClasses.  At the end of the qual
@@ -1296,6 +1334,18 @@ typedef struct StatisticExtInfo
  * that all or none of the input datatypes are collatable, so that a single
  * collation value is sufficient.)
  *
+ * Strictly speaking, deductions from an EquivalenceClass hold only within
+ * a "join domain", that is a set of relations that are innerjoined together
+ * (see JoinDomain above).  For the most part we don't need to account for
+ * this explicitly, because equality clauses from different join domains
+ * will contain Vars that are not equal() because they have different
+ * nullingrel sets, and thus we will never falsely merge ECs from different
+ * join domains.  But Var-free (pseudoconstant) expressions lack that safety
+ * feature.  We handle that by marking "const" EC members with the JoinDomain
+ * of the clause they came from; two nominally-equal const members will be
+ * considered different if they came from different JoinDomains.  This ensures
+ * no false EquivalenceClass merges will occur.
+ *
  * We also use EquivalenceClasses as the base structure for PathKeys, letting
  * us represent knowledge about different sort orderings being equivalent.
  * Since every PathKey must reference an EquivalenceClass, we will end up
@@ -1310,11 +1360,6 @@ typedef struct StatisticExtInfo
  * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
  * So we record the SortGroupRef of the originating sort clause.
  *
- * We allow equality clauses appearing below the nullable side of an outer join
- * to form EquivalenceClasses, but these have a slightly different meaning:
- * the included values might be all NULL rather than all the same non-null
- * values.  See src/backend/optimizer/README for more on that point.
- *
  * NB: if ec_merged isn't NULL, this class has been merged into another, and
  * should be ignored in favor of using the pointed-to class.
  *
@@ -1339,7 +1384,6 @@ typedef struct EquivalenceClass
 								 * for child members (see below) */
 	bool		ec_has_const;	/* any pseudoconstants in ec_members? */
 	bool		ec_has_volatile;	/* the (sole) member is a volatile expr */
-	bool		ec_below_outer_join;	/* equivalence applies below an OJ */
 	bool		ec_broken;		/* failed to generate needed clauses? */
 	Index		ec_sortref;		/* originating sortclause label, or 0 */
 	Index		ec_min_security;	/* minimum security_level in ec_sources */
@@ -1348,11 +1392,11 @@ typedef struct EquivalenceClass
 } EquivalenceClass;
 
 /*
- * If an EC contains a const and isn't below-outer-join, any PathKey depending
- * on it must be redundant, since there's only one possible value of the key.
+ * If an EC contains a constant, any PathKey depending on it must be
+ * redundant, since there's only one possible value of the key.
  */
 #define EC_MUST_BE_REDUNDANT(eclass)  \
-	((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)
+	((eclass)->ec_has_const)
 
 /*
  * EquivalenceMember - one member expression of an EquivalenceClass
@@ -1387,6 +1431,7 @@ typedef struct EquivalenceMember
 	bool		em_is_const;	/* expression is pseudoconstant? */
 	bool		em_is_child;	/* derived version for a child relation? */
 	Oid			em_datatype;	/* the "nominal type" used by the opfamily */
+	JoinDomain *em_jdomain;		/* join domain containing the source clause */
 	/* if em_is_child is true, this links to corresponding EM for top parent */
 	struct EquivalenceMember *em_parent pg_node_attr(read_write_ignore);
 } EquivalenceMember;
diff --git a/src/include/optimizer/paths.h b/src/include/optimizer/paths.h
index 1b02a1dc08..736d78ea4c 100644
--- a/src/include/optimizer/paths.h
+++ b/src/include/optimizer/paths.h
@@ -122,7 +122,7 @@ typedef bool (*ec_matches_callback_type) (PlannerInfo *root,
 
 extern bool process_equivalence(PlannerInfo *root,
 								RestrictInfo **p_restrictinfo,
-								bool below_outer_join);
+								JoinDomain *jdomain);
 extern Expr *canonicalize_ec_expression(Expr *expr,
 										Oid req_type, Oid req_collation);
 extern void reconsider_outer_join_clauses(PlannerInfo *root);
diff --git a/src/include/optimizer/planmain.h b/src/include/optimizer/planmain.h
index 3e6e60f549..5fc900737d 100644
--- a/src/include/optimizer/planmain.h
+++ b/src/include/optimizer/planmain.h
@@ -84,7 +84,6 @@ extern RestrictInfo *process_implied_equality(PlannerInfo *root,
 											  Expr *item2,
 											  Relids qualscope,
 											  Index security_level,
-											  bool below_outer_join,
 											  bool both_const);
 extern RestrictInfo *build_implied_join_equality(PlannerInfo *root,
 												 Oid opno,

---

From: Tom Lane <[email-masked]>
Date: Tue, 24 Jan 2023 14:31:27 -0500

I wrote:
> Hans Buschmann <[email-masked]> writes:
>> I just noticed your new efforts in this area.
>> I wanted to recurr to my old thread [1] considering constant propagation of quals.
>> [1]  https://www.postgresql.org/message-id/[email-masked]

> Yeah, this patch series is not yet quite up to the point of improving
> that.  That area is indeed the very next thing I want to work on, and
> I did spend some effort on it last month, but I ran out of time to get
> it working.  Maybe we'll have something there for v17.

BTW, to clarify what's going on there: what I want to do is allow
the regular equivalence-class machinery to handle deductions from
equality operators appearing in LEFT JOIN ON clauses (maybe full
joins too, but I'd be satisfied if it works for one-sided outer
joins).  I'd originally hoped that distinguishing pre-nulled from
post-nulled variables would be enough to make that safe, but it's
not.  Here's an example:

	select ... from t1 left join t2 on (t1.x = t2.y and t1.x = 1);

If we turn the generic equivclass.c logic loose on these clauses,
it will deduce t2.y = 1, which is good, and then apply t2.y = 1 at
the scan of t2, which is even better (since we might be able to turn
that into an indexscan qual).  However, it will also try to apply
t1.x = 1 at the scan of t1, and that's just wrong, because that
will eliminate t1 rows that should come through with null extension.

My current plan for making this work is to define
EquivalenceClass-generated clauses as applying within "join domains",
which are sets of inner-joined relations, and in the case of a one-sided
outer join then the join itself belongs to the same join domain as its
right-hand side --- but not to the join domain of its left-hand side.
This would allow us to push EC clauses from an outer join's qual down
into the RHS, but not into the LHS, and then anything leftover would
still have to be applied at the join.  In this example we'd have to
apply t1.x = t2.y or t1.x = 1, but not both, at the join.

I got as far as inventing join domains, in the 0012 patch of this
series, but I haven't quite finished puzzling out the clause application
rules that would be needed for this scenario.  Ordinarily an EC
containing a constant would be fully enforced at the scan level
(i.e., apply t1.x = 1 and t2.y = 1 at scan level) and generate no
additional clauses at join level; but that clearly doesn't work
anymore when some of the scans are outside the join domain.
I think that the no-constant case might need to be different too.
I have some WIP code but nothing I can show.

Also, this doesn't seem to help for full joins.  We can treat the
two sides as each being their own join domains, but then the join's
own ON clause doesn't belong to either one, since we can't throw
away rows from either side on the basis of a restriction from ON.
So it seems like we'll still need ad-hoc logic comparable to
reconsider_full_join_clause, if we want to preserve that optimization.
I'm only mildly discontented with that, but still discontented.

			regards, tom lane

---

From: "David G. Johnston" <[email-masked]>
Date: Tue, 24 Jan 2023 12:47:53 -0700

On Tue, Jan 24, 2023 at 12:31 PM Tom Lane <[email-masked]> wrote:

> >> [1]
> https://www.postgresql.org/message-id/[email-masked]
>
Is there a particular comment or README where that last conclusion is
explained so that it makes sense.  Intuitively, I would expect t1.x = 1 to
be applied during the scan of t1 - it isn't like the output of the join is
allowed to include t1 rows not matching that condition anyway.

IOW, I thought the more verbose but equivalent syntax for that was:

select ... from (select * from t1 as insub where insub.x = 1) as t1 left
join t2 on (t1.x  = t2.y)

Thanks!

David J.

---

From: Justin Pryzby <[email-masked]>
Date: Sun, 12 Feb 2023 17:58:23 -0600

> it's surprising it's had so few conflicts to date.

The patch broke this query:

select from pg_inherits inner join information_schema.element_types
right join (select from pg_constraint as sample_2) on true
on false, lateral (select scope_catalog, inhdetachpending from pg_publication_namespace limit 3);
ERROR:  could not devise a query plan for the given query