From: Andreas Joseph Krogh <andreak@officenet.no>
To: pgsql-sql@postgresql.org
Subject: Re: Alternative to INTERSECT
Date: Tue, 31 Jul 2007 19:45:10 +0000
Message-ID: <200707311945.16573.andreak@officenet.no> (raw)
In-Reply-To: <20070731135222.394da3dd@sinkhole.intrcomm.net>
References: <200707311730.51280.andreak@officenet.no>
<20070731135222.394da3dd@sinkhole.intrcomm.net>
On Tuesday 31 July 2007 18:52:22 Josh Trutwin wrote:
> 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?
Yes, as I wrote:
CREATE INDEX test_like_idx ON test USING btree
(id, field, value varchar_pattern_ops);
And I'm observing that it uses that index.
Your query doesn't cut it, let me try to explain what I'm trying to achieve:
Suppose I have the following data:
INSERT INTO test VALUES (1, 'firstname', 'andreas');
INSERT INTO test VALUES (1, 'firstname', 'joseph');
INSERT INTO test VALUES (1, 'lastname', 'krogh');
INSERT INTO test VALUES (2, 'firstname', 'andreas');
INSERT INTO test VALUES (2, 'lastname', 'noname');
The reason for why I use INTERSECT is that I want:
SELECT t.id from test t WHERE t.field = 'firstname' AND t.value
LIKE 'andrea%'
INTERSECT SELECT t.id FROM test t WHERE t.field = 'firstname' AND t.value
LIKE 'jose%'
INTERSECT SELECT t.id FROM test t WHERE t.field = 'lastname' AND t.value
LIKE 'kro%';
To return only id 1, and the query:
SELECT t.id from test t WHERE t.field = 'firstname' AND t.value
LIKE 'andrea%'
INTERSECT SELECT t.id FROM test t WHERE t.field = 'firstname' AND t.value
LIKE 'jose%'
INTERSECT SELECT t.id FROM test t WHERE t.field = 'lastname' AND t.value
LIKE 'non%';
To return no rows at all (cause nobydy's name is "andreas joseph noname").
Your suggestion doesn't cover this case.
--
AJK
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To: pgsql-sql@postgresql.org
Cc: andreak@officenet.no
Subject: Re: Alternative to INTERSECT
In-Reply-To: <200707311945.16573.andreak@officenet.no>
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