Re: plan variations: join vs. exists vs. row comparison

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Jon Nelson" <jnelson+pgsql(at)jamponi(dot)net>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-performance(at)postgresql(dot)org>
Subject: Re: plan variations: join vs. exists vs. row comparison
Date: 2011-03-07 20:24:36
Message-ID: 4D74EAA4020000250003B5AB@gw.wicourts.gov
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Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> wrote:

> What is the difference between a plain join and a semi join?

As soon as a semi join finds a match it stops looking for more.

-Kevin

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