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Commitb2c51e6

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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 righthandside 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)
1 parent4e03b82 commitb2c51e6

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‎src/backend/optimizer/README

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@@ -1,4 +1,4 @@
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$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.49 2009/02/27 22:41:37 tgl Exp $
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$PostgreSQL: pgsql/src/backend/optimizer/README,v 1.50 2009/07/21 02:02:44 tgl Exp $
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Optimizer
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=========
@@ -214,10 +214,10 @@ out of the nullable side of an outer join:
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!= (A leftjoin B on (Pab)) join C on (Pbc)
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SEMI joins work a little bit differently. A semijoin can be reassociated
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into or out of the lefthand side of another semijoin,but not into or out
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of the righthand side. Likewise, an inner join, left join, or antijoin
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can be reassociated into or out of the lefthand side of a semijoin, but
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not into or out of the righthand side.
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into or out of the lefthand side of another semijoin,left join, or
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antijoin, but not into or outof the righthand side. Likewise, an inner
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join, left join, or antijoincan be reassociated into or out of the
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lefthand side of a semijoin, butnot into or out of the righthand side.
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ANTI joins work approximately like LEFT joins, except that identity 3
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fails if the join to C is an antijoin (even if Pbc is strict, and in

‎src/backend/optimizer/plan/initsplan.c

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@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.154 2009/06/11 14:48:59 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/optimizer/plan/initsplan.c,v 1.155 2009/07/21 02:02:44 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -630,16 +630,16 @@ make_outerjoininfo(PlannerInfo *root,
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* min_lefthand + min_righthand. This is because there might be other
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* OJs below this one that this one can commute with, but we cannot
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* commute with them if we don't with this one.) Also, if the current
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* join isanantijoin, we must preserve ordering regardless of
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* strictness.
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* join isa semijoin orantijoin, we must preserve ordering
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*regardless ofstrictness.
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*
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* Note: I believe we have to insist on being strict for at least one
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* rel in the lower OJ's min_righthand, not its whole syn_righthand.
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*/
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if (bms_overlap(left_rels,otherinfo->syn_righthand))
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{
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if (bms_overlap(clause_relids,otherinfo->syn_righthand)&&
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(jointype==JOIN_ANTI||
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(jointype==JOIN_SEMI||jointype==JOIN_ANTI||
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!bms_overlap(strict_relids,otherinfo->min_righthand)))
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{
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min_lefthand=bms_add_members(min_lefthand,
@@ -655,7 +655,7 @@ make_outerjoininfo(PlannerInfo *root,
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* can interchange the ordering of the two OJs; otherwise we must add
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* lower OJ's full syntactic relset to min_righthand. Here, we must
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* preserve ordering anyway if either the current join is a semijoin,
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* or the lower OJ is an antijoin.
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* or the lower OJ iseither a semijoin oran antijoin.
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*
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* Here, we have to consider that "our join condition" includes any
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* clauses that syntactically appeared above the lower OJ and below
@@ -672,6 +672,7 @@ make_outerjoininfo(PlannerInfo *root,
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{
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if (bms_overlap(clause_relids,otherinfo->syn_righthand)||
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jointype==JOIN_SEMI||
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otherinfo->jointype==JOIN_SEMI||
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otherinfo->jointype==JOIN_ANTI||
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!otherinfo->lhs_strict||otherinfo->delay_upper_joins)
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{

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