postgres.git / summary / log / commit / refs

commit    a84e90bb249d3ece4041f46651b4de566b7f6684
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Fri Dec 22 17:08:34 2017 +0000
First released in: 9.4.16, 9.5.11, 9.6.7

    Disallow UNION/INTERSECT/EXCEPT over no columns.
    
    Since 9.4, we've allowed the syntax "select union select" and variants
    of that.  However, the planner wasn't expecting a no-column set operation
    and ended up treating the set operation as if it were UNION ALL.
    
    Pre-v10, there seem to be some executor issues that would need to be
    fixed to support such cases, and it doesn't really seem worth expending
    much effort on.  Just disallow it, instead.
    
    Per report from Victor Yegorov.
    
    Discussion: https://postgr.es/m/CAGnEbojGJrRSOgJwNGM7JSJZpVAf8xXcVPbVrGdhbVEHZ-BUMw@mail.gmail.com


 src/backend/optimizer/prep/prepunion.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index 2e55131a591..e80ad7753de 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -594,12 +594,13 @@ generate_nonunion_plan(SetOperationStmt *op, PlannerInfo *root,
 	/* Identify the grouping semantics */
 	groupList = generate_setop_grouplist(op, tlist);
 
-	/* punt if nothing to group on (can this happen?) */
+	/* punt if nothing to group on (not worth fixing in back branches) */
 	if (groupList == NIL)
-	{
-		*sortClauses = NIL;
-		return plan;
-	}
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 /* translator: %s is UNION, INTERSECT, or EXCEPT */
+				 errmsg("%s over no columns is not supported",
+						(op->op == SETOP_INTERSECT) ? "INTERSECT" : "EXCEPT")));
 
 	/*
 	 * Estimate number of distinct groups that we'll need hashtable entries
@@ -738,12 +739,12 @@ make_union_unique(SetOperationStmt *op, Plan *plan,
 	/* Identify the grouping semantics */
 	groupList = generate_setop_grouplist(op, plan->targetlist);
 
-	/* punt if nothing to group on (can this happen?) */
+	/* punt if nothing to group on (not worth fixing in back branches) */
 	if (groupList == NIL)
-	{
-		*sortClauses = NIL;
-		return plan;
-	}
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 /* translator: %s is UNION, INTERSECT, or EXCEPT */
+				 errmsg("%s over no columns is not supported", "UNION")));
 
 	/*
 	 * XXX for the moment, take the number of distinct groups as equal to the


[parent: 195516c9a6d7]