Consider a clause to be outerjoin_delayed if it references the nullable side

of any lower outer join, even if it also references the non-nullable side and
so could not get pushed below the outer join anyway.  We need this in case
the clause is an OR clause: if it doesn't get marked outerjoin_delayed,
create_or_index_quals() could pull an indexable restriction for the nullable
side out of it, leading to wrong results as demonstrated by today's bug
report from toruvinn.  (See added regression test case for an example.)

In principle this has been wrong for quite a while.  In practice I don't
think any branch before 8.3 can really show the failure, because
create_or_index_quals() will only pull out indexable conditions, and before
8.3 those were always strict.  So though we might have improperly generated
null-extended rows in the outer join, they'd get discarded from the result
anyway.  The gating factor that makes the failure visible is that 8.3
considers "col IS NULL" to be indexable.  Hence I'm not going to risk
back-patching further than 8.3.

1 files changed, 4 insertions, 3 deletions

diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index dd08b19cb83..6cfd2ab4c38 100644
--- a/src/backend/optimizer/plan/initsplan.c
+++ b/src/backend/optimizer/plan/initsplan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.139 2008/04/01 00:48:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.140 2008/06/27 20:54:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1092,14 +1092,15 @@ check_outerjoin_delay(PlannerInfo *root, Relids *relids_p,
 				(ojinfo->is_full_join &&
 				 bms_overlap(relids, ojinfo->min_lefthand)))
 			{
-				/* yes; have we included all its rels in relids? */
+				/* yes, so set the result flag */
+				outerjoin_delayed = true;
+				/* have we included all its rels in relids? */
 				if (!bms_is_subset(ojinfo->min_lefthand, relids) ||
 					!bms_is_subset(ojinfo->min_righthand, relids))
 				{
 					/* no, so add them in */
 					relids = bms_add_members(relids, ojinfo->min_lefthand);
 					relids = bms_add_members(relids, ojinfo->min_righthand);
-					outerjoin_delayed = true;
 					/* we'll need another iteration */
 					found_some = true;
 				}