Re: NOT LIKE much faster than LIKE?

From: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
To: Andrea Arcangeli <andrea(at)cpushare(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: NOT LIKE much faster than LIKE?
Date: 2006-01-11 21:02:21
Message-ID: 20060111210221.GD63175@pervasive.com
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On Wed, Jan 11, 2006 at 09:39:47PM +0100, Andrea Arcangeli wrote:
> > CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );
>
> The index only helps the above query with = 0 and not the one with != 0,
> but it seems not needed in practice.

Hrm. If you need indexing then, you'll probably have to do 2 indexes
with a WHERE clause...

CREATE INDEX ... WHERE position(...) = 0;
CREATE INDEX ... WHERE position(...) != 0;

I suspect this is because of a lack of stats for functional indexes.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461

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