From: Gregory Stark <stark@enterprisedb.com>
To: Hans Ekbrand <hans.ekbrand@sociology.gu.se>
Cc: pgsql-performance@postgresql.org
Subject: Re: mysterious difference in speed when combining two queries with OR
Date: Wed, 23 Apr 2008 09:31:39 -0400
Message-ID: <873apcu284.fsf@oxford.xeocode.com> (raw)
In-Reply-To: <20080423092205.GI11886@amin>
References: <20080423072303.GF11886@amin>
<20080423075810.GB8401@a-kretschmer.de>
<20080423085704.GG8401@a-kretschmer.de>
<20080423092205.GI11886@amin>
"Hans Ekbrand" <hans.ekbrand@sociology.gu.se> writes:
> No, I just wanted to show the time differences, I haven't used join
> before. Now that you have adviced me to, I have tried your suggestion
> to rewrite B as a union and it works good! Just as fast as the A Query!
You can even do better. If you know the two sets of mid are disjoint you can
use UNION ALL. If not you could remove the two DISTINCTs as the UNION will
take care of removing duplicates.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's On-Demand Production Tuning
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To: pgsql-performance@postgresql.org
Cc: stark@enterprisedb.com, hans.ekbrand@sociology.gu.se
Subject: Re: mysterious difference in speed when combining two queries with OR
In-Reply-To: <873apcu284.fsf@oxford.xeocode.com>
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