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Re: BUG #3494: may be Query Error: subplan does not executed

From: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Sergey Burladyan <eshkinkot(at)gmail(dot)com>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #3494: may be Query Error: subplan does not executed
Date: 2007-07-31 09:10:14
Message-ID: 46AEFC76.4050001@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-bugs
Tom Lane wrote:
> It appears that join_clause_is_redundant() is rejecting the clause as
> redundant.  I suppose some part of that machinery gets confused by the
> fact that the RHS of the clause references both relations.  The
> EquivalenceClass rewrite cleaned this whole area up greatly, so no
> surprise that the bug is gone in HEAD.  No time to look at it more now.

Yeah, that's it.

I don't understand that code very well. Why does it think that the right
pathkeys of "test1.id = test2.id" and "test1.id = test1.id+test2.id" are
equal?

Checking for overlapping left and right relation sets in
join_clause_is_redundant seems to fix the problem, though I'm not sure
if there's some other cases that that doesn't catch.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

Attachment: fix-3493.patch
Description: text/x-diff (2.1 KB)

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