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Re: BUG #5084: Query gives different number of rows depending on ORDER BY

From: Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>
To: tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane), heikki(dot)linnakangas(at)enterprisedb(dot)com (Heikki Linnakangas), Bernt Marius Johnsen <bernt(dot)johnsen(at)sun(dot)com>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #5084: Query gives different number of rows depending on ORDER BY
Date: 2009-09-29 00:28:13
Message-ID: 87k4zik31e.fsf@news-spur.riddles.org.uk (view raw or flat)
Thread:
Lists: pgsql-bugs
>>>>> "Tom" == Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

 Tom> I'm inclined to think that the best solution is to have
 Tom> process_equivalence just reject any clauses that have equal()
 Tom> left and right sides, ie, throw them back to be processed as
 Tom> ordinary non-equivalence clauses.

 >> Hmm. Is it ever possible for mergejoinable operators to be
 >> non-strict?  Does that matter?

 Tom> I'm not sure. ISTR that nodeMergejoin makes some effort to
 Tom> support such operators, but the btree code doesn't really.  In
 Tom> any case, it doesn't matter.  Leaving the clause out of the
 Tom> equivalence machinery is certainly safe; at worst we'll end up
 Tom> with a redundant test or two in the final plan.

Yeah, and clearly leaving in that kind of redundant test is no big
deal.

-- 
Andrew (irc:RhodiumToad)

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