Improve parser's and planner's handling of set-returning functions.

Teach the parser to reject misplaced set-returning functions during parse
analysis using p_expr_kind, in much the same way as we do for aggregates
and window functions (cf commit eaccfded9).  While this isn't complete
(it misses nesting-based restrictions), it's much better than the previous
error reporting for such cases, and it allows elimination of assorted
ad-hoc expression_returns_set() error checks.  We could add nesting checks
later if it seems important to catch all cases at parse time.

There is one case the parser will now throw error for although previous
versions allowed it, which is SRFs in the tlist of an UPDATE.  That never
behaved sensibly (since it's ill-defined which generated row should be
used to perform the update) and it's hard to see why it should not be
treated as an error.  It's a release-note-worthy change though.

Also, add a new Query field hasTargetSRFs reporting whether there are
any SRFs in the targetlist (including GROUP BY/ORDER BY expressions).
The parser can now set that basically for free during parse analysis,
and we can use it in a number of places to avoid expression_returns_set
searches.  (There will be more such checks soon.)  In some places, this
allows decontorting the logic since it's no longer expensive to check for
SRFs in the tlist --- so I made the checks parallel to the handling of
hasAggs/hasWindowFuncs wherever it seemed appropriate.

catversion bump because adding a Query field changes stored rules.

Andres Freund and Tom Lane

Discussion: <24639.1473782855@sss.pgh.pa.us>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index e28a8dc533e..74e42451228 100644
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -650,6 +650,11 @@ rel_is_distinct_for(PlannerInfo *root, RelOptInfo *rel, List *clause_list)
 bool
 query_supports_distinctness(Query *query)
 {
+	/* we don't cope with SRFs, see comment below */
+	if (query->hasTargetSRFs)
+		return false;
+
+	/* check for features we can prove distinctness with */
 	if (query->distinctClause != NIL ||
 		query->groupClause != NIL ||
 		query->groupingSets != NIL ||
@@ -695,7 +700,7 @@ query_is_distinct_for(Query *query, List *colnos, List *opids)
 	 * specified columns, since those must be evaluated before de-duplication;
 	 * but it doesn't presently seem worth the complication to check that.)
 	 */
-	if (expression_returns_set((Node *) query->targetList))
+	if (query->hasTargetSRFs)
 		return false;
 
 	/*