From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
To: Itai Zukerman <zukerman@math-hat.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: count(*), EXISTS, indexes
Date: Fri, 11 Apr 2003 15:12:09 -0700 (PDT)
Message-ID: <20030411150926.C838-100000@megazone23.bigpanda.com> (raw)
In-Reply-To: <87smsora9b.fsf@matt.w80.math-hat.com>
On Fri, 11 Apr 2003, Itai Zukerman wrote:
> > CREATE TABLE A (x int PRIMARY KEY, real v);
> > CREATE TABLE B (x int);
> >
> > I'd like to calculate:
> >
> > SELECT sum(v) FROM A WHERE EXISTS (SELECT 1 FROM B WHERE A.x=B.x);
>
> This seems to be a reasonably-performing workaround:
>
> SELECT DISTINCT x INTO TEMP C FROM A,B WHERE A.x=B.x;
> SELECT sum(v) FROM A,C WHERE A.x=C.x;
Hmm, given that, would something like:
select sum(v) from
(select distinct on(x) x,v from a,b where a.x=b.x) as foo;
work?
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To: pgsql-sql@postgresql.org
Cc: sszabo@megazone23.bigpanda.com, zukerman@math-hat.com
Subject: Re: count(*), EXISTS, indexes
In-Reply-To: <20030411150926.C838-100000@megazone23.bigpanda.com>
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