From: Tom Lane <tgl@sss.pgh.pa.us>
To: Markus Bertheau <twanger@bluetwanger.de>
Cc: pgsql-sql <pgsql-sql@postgresql.org>
Subject: Re: Difference between IN and JOIN
Date: Mon, 04 Oct 2004 10:17:16 -0400
Message-ID: <20688.1096899436@sss.pgh.pa.us> (raw)
In-Reply-To: <1096879190.2651.8.camel@dicaprio.akademie1.de>
References: <1096879190.2651.8.camel@dicaprio.akademie1.de>
Markus Bertheau <twanger@bluetwanger.de> writes:
> I lately wondered if there is a difference between a JOIN and a IN in
> queries similar to the following:
> SELECT f1 FROM t1 JOIN t2 ON (t.f2 = t2.f2) WHERE t2.f3 = x
> SELECT f1 FROM t1 WHERE t1.f2 IN (SELECT f2 FROM t2 WHERE f3 = x)
> As I see it there's no semantic difference between the two.
There's plenty of difference, if t2 contains repeated occurrences of f2
values.
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, twanger@bluetwanger.de
Subject: Re: Difference between IN and JOIN
In-Reply-To: <20688.1096899436@sss.pgh.pa.us>
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