diff options
Diffstat (limited to 'src/backend/optimizer/path/allpaths.c')
| -rw-r--r-- | src/backend/optimizer/path/allpaths.c | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c index c8335868133..b13371e00eb 100644 --- a/src/backend/optimizer/path/allpaths.c +++ b/src/backend/optimizer/path/allpaths.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.171 2008/06/27 03:56:55 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/allpaths.c,v 1.172 2008/08/02 21:31:59 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -963,11 +963,12 @@ compare_tlist_datatypes(List *tlist, List *colTypes, * * 4. If the subquery uses DISTINCT ON, we must not push down any quals that * refer to non-DISTINCT output columns, because that could change the set - * of rows returned. This condition is vacuous for DISTINCT, because then - * there are no non-DISTINCT output columns, but unfortunately it's fairly - * expensive to tell the difference between DISTINCT and DISTINCT ON in the - * parsetree representation. It's cheaper to just make sure all the Vars - * in the qual refer to DISTINCT columns. + * of rows returned. (This condition is vacuous for DISTINCT, because then + * there are no non-DISTINCT output columns, so we needn't check. But note + * we are assuming that the qual can't distinguish values that the DISTINCT + * operator sees as equal. This is a bit shaky but we have no way to test + * for the case, and it's unlikely enough that we shouldn't refuse the + * optimization just because it could theoretically happen.) * * 5. We must not push down any quals that refer to subselect outputs that * return sets, else we'd introduce functions-returning-sets into the @@ -1030,8 +1031,8 @@ qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual, Assert(tle != NULL); Assert(!tle->resjunk); - /* If subquery uses DISTINCT or DISTINCT ON, check point 4 */ - if (subquery->distinctClause != NIL && + /* If subquery uses DISTINCT ON, check point 4 */ + if (subquery->hasDistinctOn && !targetIsInSortList(tle, InvalidOid, subquery->distinctClause)) { /* non-DISTINCT column, so fail */ |