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Fix a thinko in join_is_legal: when we decide we can implement a semijoin

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by unique-ifying the RHS and then inner-joining to some other relation,
that is not grounds for violating the RHS of some other outer join.
Noticed while regression-testing new GEQO code, which will blindly follow
any path that join_is_legal says is legal, and then complain later if that
leads to a dead end.

I'm not certain that this can result in any visible failure in 8.4: the
mistake may always be masked by the fact that subsequent attempts to join
the rest of the RHS of the other join will fail.  But I'm not certain it
can't, either, and it's definitely not operating as intended.  So back-patch.

The added regression test depends on the new no-failures-allowed logic
that I'm about to commit in GEQO, so no point back-patching that.
This commit is contained in:
Tom Lane
2009-07-19 20:32:48 +00:00
parent 011eae60ef
commit a43b190e3c
3 changed files with 36 additions and 3 deletions
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10
src/test/regress/sql/join.sql
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@@ -343,6 +343,16 @@ select count(*) from tenk1 x where
x.unique1 = 0 and
x.unique1 in (select aa.f1 from int4_tbl aa,float8_tbl bb where aa.f1=bb.f1);
-- try that with GEQO too
begin;
set geqo = on;
set geqo_threshold = 2;
select count(*) from tenk1 x where
x.unique1 in (select a.f1 from int4_tbl a,float8_tbl b where a.f1=b.f1) and
x.unique1 = 0 and
x.unique1 in (select aa.f1 from int4_tbl aa,float8_tbl bb where aa.f1=bb.f1);
rollback;
--
-- Clean up