From: Richard Huxton <dev@archonet.com>
To: Sean Davis <sdavis2@mail.nih.gov>
Cc: PostgreSQL SQL <pgsql-sql@postgresql.org>
Subject: Re: Self-referencing table question
Date: Tue, 22 Mar 2005 20:59:58 +0000
Message-ID: <4240874E.2080301@archonet.com> (raw)
In-Reply-To: <7e154914b76fb1a7c55912b621400860@mail.nih.gov>
References: <0af8c6d3baaf3d4a6d918df294019507@mail.nih.gov>
<7e154914b76fb1a7c55912b621400860@mail.nih.gov>
Sean Davis wrote:
> I answer my own question, if only for my own records. The following
> query is about 5-6 times faster than the original. Of course, if
> anyone else has other ideas, I'd be happy to hear them.
>
> Sean
>
> explain analyze select from_id,to_id,val from exprsdb.correlation where
> from_id in (select to_id from exprsdb.correlation where from_id=2424
> order by val desc limit 100) and to_id in (select to_id from
> exprsdb.correlation where from_id=2424 order by val desc limit 100) and
> val>0.6 and to_id<from_id;
Might not be any faster, but you can do this as a self-join with subquery:
SELECT c1.from_id, c1.to_id, c1.val
FROM
correlation c1,
(
SELECT to_id FROM correlation WHERE from_id=2424
ORDER BY val DESC LIMIT 100
) AS c2
(
SELECT to_id FROM correlation WHERE from_id=2424
ORDER BY val DESC LIMIT 100
) AS c3
WHERE
c1.from_id = c2.to_id
AND c1.to_id = c3.to_id
AND c1.val > 0.5
AND c1.to_id < from_id
;
I think PG should be smart enough nowadays to figure out these two
queries are basically the same.
--
Richard Huxton
Archonet Ltd
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To: pgsql-sql@postgresql.org
Cc: dev@archonet.com, sdavis2@mail.nih.gov
Subject: Re: Self-referencing table question
In-Reply-To: <4240874E.2080301@archonet.com>
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