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Re: Get Postgres to use multiple proc cores? - Mailing list pgsql-admin

From Kevin Grittner
Subject Re: Get Postgres to use multiple proc cores?
Date
Msg-id 4CD3E5B8020000250003735A@gw.wicourts.gov
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In response to Re: Get Postgres to use multiple proc cores?  ("Oliveiros d'Azevedo Cristina" <oliveiros.cristina@marktest.pt>)
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"Oliveiros d'Azevedo Cristina" <oliveiros.cristina@marktest.pt>
wrote:

> What is faster? A JOIN or a WHERE a IN (SELECT ... )

On 8.4 and later an EXISTS or NOT EXISTS will use semi-join or
anti-join (respectively).  These should usually be much faster than
the IN (SELECT DISTINCT ... ) technique.  Be careful of the
difference in semantics between NOT EXISTS and NOT IN if any of the
columns involved in the matching can be null -- they are *not* the
same thing.

-Kevin

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