From: Dimitri Fontaine <dfontaine@hi-media.com>
To: pgsql-performance@postgresql.org
Cc: Moritz Onken <onken@houseofdesign.de>
Subject: Re: Planner should use index on a LIKE 'foo%' query
Date: Mon, 30 Jun 2008 12:20:40 +0200
Message-ID: <200806301220.43392.dfontaine@hi-media.com> (raw)
In-Reply-To: <287E4428-BECC-46D6-BC47-EA94EA0121F0@houseofdesign.de>
References: <287E4428-BECC-46D6-BC47-EA94EA0121F0@houseofdesign.de>
Hi,
Le samedi 28 juin 2008, Moritz Onken a écrit :
> select count(*)
> from result
> where exists
> (select * from item where item.url LIKE result.url || '%' limit 1);
>
> which basically returns the number of items which exist in table
> result and match a URL in table item by its prefix.
It seems you could benefit from the prefix project, which support indexing
your case of prefix searches. Your query would then be:
SELECT count(*) FROM result r JOIN item i ON r.url @> i.url;
The result.url column would have to made of type prefix_range, which casts
automatically to text when needed.
Find out more about the prefix projects at those urls:
http://pgfoundry.org/projects/prefixhttp://prefix.projects.postgresql.org/README.html
Regards,
--
dim
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To: pgsql-performance@postgresql.org
Cc: dfontaine@hi-media.com, onken@houseofdesign.de
Subject: Re: Planner should use index on a LIKE 'foo%' query
In-Reply-To: <200806301220.43392.dfontaine@hi-media.com>
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