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Commitc372671

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Fix generate_union_paths for non-sortable types.
The previous logic would fail to set groupList whengrouping_is_sortable() returned false, which could cause queriesto return wrong answers when some columns were not sortable.David Rowley, reviewed by Heikki Linnakangas and Álvaro Herrera.Reported by Hubert "depesz" Lubaczewski.Discussion:http://postgr.es/m/Zktzf926vslR35Fv@depesz.comDiscussion:http://postgr.es/m/CAApHDvra=c8_zZT0J-TftByWN2Y+OJfnjNJFg4Dfdi2s+QzmqA@mail.gmail.com
1 parent12933dc commitc372671

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3 files changed

+31
-9
lines changed

3 files changed

+31
-9
lines changed

‎src/backend/optimizer/prep/prepunion.c

Lines changed: 12 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -498,7 +498,7 @@ generate_recursion_path(SetOperationStmt *setOp, PlannerInfo *root,
498498
* interesting_pathkeys: if not NIL, also include paths that suit these
499499
* pathkeys, sorting any unsorted paths as required.
500500
* *pNumGroups: if not NULL, we estimate the number of distinct groups
501-
*in the result, and store it there
501+
*in the result, and store it there.
502502
*/
503503
staticvoid
504504
build_setop_child_paths(PlannerInfo*root,RelOptInfo*rel,
@@ -714,7 +714,7 @@ generate_union_paths(SetOperationStmt *op, PlannerInfo *root,
714714
List*groupList=NIL;
715715
Path*apath;
716716
Path*gpath=NULL;
717-
booltry_sorted;
717+
booltry_sorted= false;
718718
List*union_pathkeys=NIL;
719719

720720
/*
@@ -740,18 +740,21 @@ generate_union_paths(SetOperationStmt *op, PlannerInfo *root,
740740
tlist_list,refnames_tlist);
741741
*pTargetList=tlist;
742742

743-
/* For for UNIONs (not UNION ALL), try sorting, if sorting is possible */
744-
try_sorted= !op->all&&grouping_is_sortable(op->groupClauses);
745-
746-
if (try_sorted)
743+
/* For UNIONs (not UNION ALL), try sorting, if sorting is possible */
744+
if (!op->all)
747745
{
748746
/* Identify the grouping semantics */
749747
groupList=generate_setop_grouplist(op,tlist);
750748

751-
/* Determine the pathkeys for sorting by the whole target list */
752-
union_pathkeys=make_pathkeys_for_sortclauses(root,groupList,tlist);
749+
if (grouping_is_sortable(op->groupClauses))
750+
{
751+
try_sorted= true;
752+
/* Determine the pathkeys for sorting by the whole target list */
753+
union_pathkeys=make_pathkeys_for_sortclauses(root,groupList,
754+
tlist);
753755

754-
root->query_pathkeys=union_pathkeys;
756+
root->query_pathkeys=union_pathkeys;
757+
}
755758
}
756759

757760
/*

‎src/test/regress/expected/union.out

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -815,6 +815,19 @@ select x from (values (row(1, 2)), (row(1, 3))) _(x) except select x from (value
815815
(1,3)
816816
(1 row)
817817

818+
-- non-sortable type
819+
-- Ensure we get a HashAggregate plan. Keep enable_hashagg=off to ensure
820+
-- there's no chance of a sort.
821+
explain (costs off) select '123'::xid union select '123'::xid;
822+
QUERY PLAN
823+
---------------------------
824+
HashAggregate
825+
Group Key: ('123'::xid)
826+
-> Append
827+
-> Result
828+
-> Result
829+
(5 rows)
830+
818831
reset enable_hashagg;
819832
--
820833
-- Mixed types

‎src/test/regress/sql/union.sql

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -244,6 +244,12 @@ explain (costs off)
244244
select xfrom (values (row(1,2)), (row(1,3))) _(x) exceptselect xfrom (values (row(1,2)), (row(1,4))) _(x);
245245
select xfrom (values (row(1,2)), (row(1,3))) _(x) exceptselect xfrom (values (row(1,2)), (row(1,4))) _(x);
246246

247+
-- non-sortable type
248+
249+
-- Ensure we get a HashAggregate plan. Keep enable_hashagg=off to ensure
250+
-- there's no chance of a sort.
251+
explain (costs off)select'123'::xidunionselect'123'::xid;
252+
247253
reset enable_hashagg;
248254

249255
--

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