From: Andreas Joseph Krogh <andreak@officenet.no>
To: Gregory Stark <stark@enterprisedb.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: PG won't use index on ORDER BY <expression>
Date: Thu, 9 Aug 2007 22:38:46 +0200
Message-ID: <200708092238.46284.andreak@officenet.no> (raw)
In-Reply-To: <87fy2s1nrd.fsf@oxford.xeocode.com>
References: <200708092018.44111.andreak@officenet.no>
<87fy2s1nrd.fsf@oxford.xeocode.com>
On Thursday 09 August 2007 22:00:54 Gregory Stark wrote:
> "Andreas Joseph Krogh" <andreak@officenet.no> writes:
> > I create an index:
> > CREATE INDEX person_lowerfullname_idx ON
> > person((lower(COALESCE(firstname, '')) || lower(COALESCE(lastname, '')))
> > varchar_pattern_ops);
>
> Why are you declaring it using the varchar_pattern_ops?
>
> The default operator set is the one you want for handling ordering. The
> pattern_ops operator set is for handling things like x LIKE 'foo%'
Ooops, just fugured that out. But - it still doesn't use the index if I remove
the "varchar_pattern_ops". I solved it by adding a function:
CREATE OR REPLACE FUNCTION concat_lower(varchar, varchar) RETURNS varchar AS
$$
SELECT lower(coalesce($1, '')) || lower(coalesce($2, ''))
$$ LANGUAGE SQL IMMUTABLE;
And than creating an index:
CREATE INDEX person_lowerfullname_idx ON person(concat_lower(firstname,
lastname));
Another question then: Why doesn't "varchar_pattern_ops" handle ordering? This
means I need 2 indexes on the columns I want to match with LIKE and ORDER BY.
Just doesn't seem right to need 2 "similar" indexes...
--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
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To: pgsql-sql@postgresql.org
Cc: andreak@officenet.no, stark@enterprisedb.com
Subject: Re: PG won't use index on ORDER BY <expression>
In-Reply-To: <200708092238.46284.andreak@officenet.no>
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