From: Tom Lane <tgl@sss.pgh.pa.us>
To: johno <jan.suchal@gmail.com>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow query with indexed ORDER BY and LIMIT when using OR'd
 conditions
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Comments: In-reply-to johno <jan.suchal@gmail.com>
 message dated "Tue, 22 Jul 2014 07:57:08 +0200"
Date: Tue, 22 Jul 2014 02:15:29 -0400
Message-ID: <11612.1406009729@sss.pgh.pa.us>
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johno <jan.suchal@gmail.com> writes:
> On Tue, Jul 22, 2014 at 4:53 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> johno <jan.suchal@gmail.com> writes:
>>> The obvious query is
>>> SELECT * FROM register_uz_accounting_entities
>>> WHERE effective_on > '2014-07-11' OR (effective_on = '2014-07-11' AND
>>> id > 1459)
>>> ORDER BY effective_on, id
>>> LIMIT 100

>> A more readily optimizable query is
>> SELECT * FROM register_uz_accounting_entities
>> WHERE (effective_on, id) > ('2014-07-11'::date, 1459)
>> ORDER BY effective_on, id
>> LIMIT 100

> Yes, but that query has completely different semantics - I can't change
> that.

No, it doesn't.  Read it again ... or read up on row comparisons,
if you're unfamiliar with that notation.  The above queries are
exactly equivalent per spec.

			regards, tom lane


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