From b2c51e6eba1d8b3b139c529df3703b37952b5a3d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 21 Jul 2009 02:02:44 +0000
Subject: [PATCH] Fix another semijoin-ordering bug. We already knew that we
couldn't reorder a semijoin into or out of the righthand side of another
semijoin, but actually it doesn't work to reorder it into or out of the
righthand side of a left or antijoin, either. Per bug #4906 from Mathieu
Fenniak.
This was sloppy thinking on my part. This identity does work:
( A left join B on (Pab) ) semijoin C on (Pac)
==
( A semijoin C on (Pac) ) left join B on (Pab)
but I failed to see that that doesn't mean this does:
( A left join B on (Pab) ) semijoin C on (Pbc)
!=
A left join ( B semijoin C on (Pbc) ) on (Pab)
---
src/backend/optimizer/README | 10 +++++-----
src/backend/optimizer/plan/initsplan.c | 11 ++++++-----
2 files changed, 11 insertions(+), 10 deletions(-)
diff --git a/src/backend/optimizer/README b/src/backend/optimizer/README
index a3ce21b690e..f406e642db3 100644
--- a/src/backend/optimizer/README
+++ b/src/backend/optimizer/README
@@ -1,4 +1,4 @@
-$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.49 2009/02/27 22:41:37 tgl Exp $
+$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.50 2009/07/21 02:02:44 tgl Exp $
Optimizer
=========
@@ -214,10 +214,10 @@ out of the nullable side of an outer join:
!= (A leftjoin B on (Pab)) join C on (Pbc)
SEMI joins work a little bit differently. A semijoin can be reassociated
-into or out of the lefthand side of another semijoin, but not into or out
-of the righthand side. Likewise, an inner join, left join, or antijoin
-can be reassociated into or out of the lefthand side of a semijoin, but
-not into or out of the righthand side.
+into or out of the lefthand side of another semijoin, left join, or
+antijoin, but not into or out of the righthand side. Likewise, an inner
+join, left join, or antijoin can be reassociated into or out of the
+lefthand side of a semijoin, but not into or out of the righthand side.
ANTI joins work approximately like LEFT joins, except that identity 3
fails if the join to C is an antijoin (even if Pbc is strict, and in
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
index 8a189d4443d..9ea928ed9d4 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 1.154 2009/06/11 14:48:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.155 2009/07/21 02:02:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -630,8 +630,8 @@ make_outerjoininfo(PlannerInfo *root,
* min_lefthand + min_righthand. This is because there might be other
* OJs below this one that this one can commute with, but we cannot
* commute with them if we don't with this one.) Also, if the current
- * join is an antijoin, we must preserve ordering regardless of
- * strictness.
+ * join is a semijoin or antijoin, we must preserve ordering
+ * regardless of strictness.
*
* Note: I believe we have to insist on being strict for at least one
* rel in the lower OJ's min_righthand, not its whole syn_righthand.
@@ -639,7 +639,7 @@ make_outerjoininfo(PlannerInfo *root,
if (bms_overlap(left_rels, otherinfo->syn_righthand))
{
if (bms_overlap(clause_relids, otherinfo->syn_righthand) &&
- (jointype == JOIN_ANTI ||
+ (jointype == JOIN_SEMI || jointype == JOIN_ANTI ||
!bms_overlap(strict_relids, otherinfo->min_righthand)))
{
min_lefthand = bms_add_members(min_lefthand,
@@ -655,7 +655,7 @@ make_outerjoininfo(PlannerInfo *root,
* can interchange the ordering of the two OJs; otherwise we must add
* lower OJ's full syntactic relset to min_righthand. Here, we must
* preserve ordering anyway if either the current join is a semijoin,
- * or the lower OJ is an antijoin.
+ * or the lower OJ is either a semijoin or an antijoin.
*
* Here, we have to consider that "our join condition" includes any
* clauses that syntactically appeared above the lower OJ and below
@@ -672,6 +672,7 @@ make_outerjoininfo(PlannerInfo *root,
{
if (bms_overlap(clause_relids, otherinfo->syn_righthand) ||
jointype == JOIN_SEMI ||
+ otherinfo->jointype == JOIN_SEMI ||
otherinfo->jointype == JOIN_ANTI ||
!otherinfo->lhs_strict || otherinfo->delay_upper_joins)
{
--
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