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Re: index usage in not like

From: Thom Brown <thombrown(at)gmail(dot)com>
To: AI Rumman <rummandba(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: index usage in not like
Date: 2010-02-18 12:00:29
Message-ID: bddc86151002180400n920f56ah9fa3d68156c6b24a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 18 February 2010 11:55, AI Rumman <rummandba(at)gmail(dot)com> wrote:
> "Not like" operation does not use index.
>
> select * from vtiger_contactscf where lower(cf_1253) not like
> lower('Former%')
>
> I created index on lower(cf_1253).
>
> How can I ensure index usage in not like operation?
> Anyone please help.
>

How many rows do you have in your table?  If there are relatively few,
it probably guesses it to be cheaper to do a sequential scan and
calculate lower values on-the-fly rather than bother with the index.

Thom

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