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Fix another semijoin-ordering bug. We already knew that we couldn't

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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)
This commit is contained in:
Tom Lane
2009-07-21 02:02:44 +00:00
parent 4e03b827ee
commit b2c51e6eba
2 changed files with 11 additions and 10 deletions
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11
src/backend/optimizer/plan/initsplan.c
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@@ -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)
{