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Switch the planner over to treating qualifications of a JOIN_SEMI join as

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though it is an inner rather than outer join type.  This essentially means
that we don't bother to separate "pushed down" qual conditions from actual
join quals at a semijoin plan node; which is okay because the restrictions of
SQL syntax make it impossible to have a pushed-down qual that references the
inner side of a semijoin.  This allows noticeably better optimization of
IN/EXISTS cases than we had before, since the equivalence-class machinery can
now use those quals.  Also fix a couple of other mistakes that had essentially
disabled the ability to unique-ify the inner relation and then join it to just
a subset of the left-hand relations.  An example case using the regression
database is

select * from tenk1 a, tenk1 b
where (a.unique1,b.unique2) in (select unique1,unique2 from tenk1 c);

which is planned reasonably well by 8.3 and earlier but had been forcing a
cartesian join of a/b in CVS HEAD.
This commit is contained in:
Tom Lane
2008-11-22 22:47:06 +00:00
parent 86422cbbfc
commit 8309d006cb
6 changed files with 87 additions and 34 deletions
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4
src/backend/optimizer/path/joinpath.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.118 2008/10/04 21:56:53 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/path/joinpath.c,v 1.119 2008/11/22 22:47:06 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -744,12 +744,12 @@ hash_inner_and_outer(PlannerInfo *root,
switch (jointype)
{
case JOIN_INNER:
case JOIN_SEMI:
case JOIN_UNIQUE_OUTER:
case JOIN_UNIQUE_INNER:
isouterjoin = false;
break;
case JOIN_LEFT:
case JOIN_SEMI:
case JOIN_ANTI:
isouterjoin = true;
break;