postgres.git / summary / log / commit / refs
commit 28a61fc6c58fbfb83e416411f55e7d6ec47279ff
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat Sep 19 19:11:26 2020 +0000
First released in: 14.0
Remove precedence hacks no longer needed without postfix operators.
It's no longer necessary to assign explicit precedences to GENERATED,
NULL_P, PRESERVE, or STRIP_P.
Actually, we don't need to assign precedence to IDENT either; that was
really just there to govern the behavior of target_el's "a_expr IDENT"
production, which no longer ends with that terminal. However, it seems
like a good idea to continue to do so, because it provides a reference
point for a precedence level that we can assign to other unreserved
keywords that lack a natural precedence level.
Research by Peter Eisentraut and John Naylor; comment rewrite by me.
Discussion: https://postgr.es/m/38ca86db-42ab-9b48-2902-337a0d6b8311@2ndquadrant.com
src/backend/parser/gram.y | 34 +++++++++++++++-------------------
1 file changed, 15 insertions(+), 19 deletions(-)
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index 017940bdcd6..17653ef3a79 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -744,22 +744,15 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
%nonassoc BETWEEN IN_P LIKE ILIKE SIMILAR NOT_LA
%nonassoc ESCAPE /* ESCAPE must be just above LIKE/ILIKE/SIMILAR */
/*
- * To support target_el without AS, we must give IDENT an explicit priority
- * between ESCAPE and Op. We can safely assign the same priority to
- * various unreserved keywords as needed to resolve ambiguities (this can't
- * have any bad effects since obviously the keywords will still behave the
- * same as if they weren't keywords). We need to do this:
- * for PARTITION, RANGE, ROWS, GROUPS to support opt_existing_window_name;
- * for RANGE, ROWS, GROUPS so that they can follow a_expr without creating
- * postfix-operator problems;
- * for GENERATED so that it can follow b_expr;
- * and for NULL so that it can follow b_expr in ColQualList without creating
- * postfix-operator problems.
+ * To support target_el without AS, it used to be necessary to assign IDENT an
+ * explicit precedence just less than Op. While that's not really necessary
+ * since we removed postfix operators, it's still helpful to do so because
+ * there are some other unreserved keywords that need precedence assignments.
+ * If those keywords have the same precedence as IDENT then they clearly act
+ * the same as non-keywords, reducing the risk of unwanted precedence effects.
*
- * To support CUBE and ROLLUP in GROUP BY without reserving them, we give them
- * an explicit priority lower than '(', so that a rule with CUBE '(' will shift
- * rather than reducing a conflicting rule that takes CUBE as a function name.
- * Using the same precedence as IDENT seems right for the reasons given above.
+ * We need to do this for PARTITION, RANGE, ROWS, and GROUPS to support
+ * opt_existing_window_name (see comment there).
*
* The frame_bound productions UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING
* are even messier: since UNBOUNDED is an unreserved keyword (per spec!),
@@ -769,9 +762,14 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
* appear to cause UNBOUNDED to be treated differently from other unreserved
* keywords anywhere else in the grammar, but it's definitely risky. We can
* blame any funny behavior of UNBOUNDED on the SQL standard, though.
+ *
+ * To support CUBE and ROLLUP in GROUP BY without reserving them, we give them
+ * an explicit priority lower than '(', so that a rule with CUBE '(' will shift
+ * rather than reducing a conflicting rule that takes CUBE as a function name.
+ * Using the same precedence as IDENT seems right for the reasons given above.
*/
-%nonassoc UNBOUNDED /* ideally should have same precedence as IDENT */
-%nonassoc IDENT GENERATED NULL_P PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
+%nonassoc UNBOUNDED /* ideally would have same precedence as IDENT */
+%nonassoc IDENT PARTITION RANGE ROWS GROUPS PRECEDING FOLLOWING CUBE ROLLUP
%left Op OPERATOR /* multi-character ops and user-defined operators */
%left '+' '-'
%left '*' '/' '%'
@@ -792,8 +790,6 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
* left-associativity among the JOIN rules themselves.
*/
%left JOIN CROSS LEFT FULL RIGHT INNER_P NATURAL
-/* kluge to keep xml_whitespace_option from causing shift/reduce conflicts */
-%right PRESERVE STRIP_P
%%
[parent: 8354e7b27ebe]