From: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
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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 |
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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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