Date: Tue, 31 Jul 2007 13:52:22 -0500
From: Josh Trutwin <josh@trutwins.homeip.net>
To: pgsql-sql@postgresql.org
Subject: Re: Alternative to INTERSECT
Message-ID: <20070731135222.394da3dd@sinkhole.intrcomm.net>
In-Reply-To: <200707311730.51280.andreak@officenet.no>
References: <200707311730.51280.andreak@officenet.no>
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On Tue, 31 Jul 2007 17:30:51 +0000
Andreas Joseph Krogh <andreak@officenet.no> wrote:

> Hi all. I have the following schema:
> 
> CREATE TABLE test (
>     id integer NOT NULL,
>     field character varying NOT NULL,
>     value character varying NOT NULL
> );
> 
> ALTER TABLE ONLY test
>     ADD CONSTRAINT test_id_key UNIQUE (id, field, value);
> 
> CREATE INDEX test_like_idx ON test USING btree (id, field, value 
> varchar_pattern_ops);
> 
> Using INTERSECT I want to retrieve the rows matching (pseudo-code)
> "firstname LIKE ('andrea%' OR 'jose%') AND lastname LIKE 'kro%'"

Why not:

WHERE (t.field = lastname AND t.value LIKE 'kro%')
   OR (t.field = firsname AND (
       t.value LIKE 'jose%' OR t.value LIKE 'andrea%')
       )

Not tested.  If you're having performance problems is probably less
like that the INTERSECT is the problem with all those LIKE's in
there?  Is t.value indexed?

Josh