From: | "Leeuw van der, Tim" <tim(dot)leeuwvander(at)nl(dot)unisys(dot)com> |
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To: | "Eric Jain" <Eric(dot)Jain(at)isb-sib(dot)ch>, "pgsql-performance" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: UPDATE with subquery too slow |
Date: | 2004-02-17 12:49:29 |
Message-ID: | DD0DC14935B1D211981A00105A1B28DB0A7B4D63@NL-ASD-EXCH-1 |
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Thread: | |
Lists: | pgsql-performance |
Hi,
This is not going to answer your question of course but did you already try to do this in 2 steps?
You said that the subquery itself doesn't take very long, so perhaps you can create a temporary table based on the subquery, then in the update do a join with the temporary table?
This might not be desirable in the end, but it might be useful just to check the performance of it.
And - isn't it an option to upgrade to 7.4.1 instead?
regards,
--Tim
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-----Original Message-----
From: pgsql-performance-owner(at)postgresql(dot)org
[mailto:pgsql-performance-owner(at)postgresql(dot)org]On Behalf Of Eric Jain
Sent: dinsdag 17 februari 2004 13:38
To: pgsql-performance
Subject: [PERFORM] UPDATE with subquery too slow
I can't get the following statement to complete with reasonable time.
I've had it running for over ten hours without getting anywhere. I
suspect (hope) there may be a better way to accomplish what I'm trying
to do (set fields containing unique values to null):
UPDATE requests
SET session = NULL
WHERE session IN
(
SELECT session
FROM requests
GROUP BY session
HAVING COUNT(*) = 1
);
[...]
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