From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Kellerer <spam_eater@gmx.net>
cc: pgsql-sql@postgresql.org
Subject: Re: DELETE using an outer join
In-reply-to: <ju8veb$dkn$1@dough.gmane.org>
References: <ju8veb$dkn$1@dough.gmane.org>
Comments: In-reply-to Thomas Kellerer <spam_eater@gmx.net>
	message dated "Thu, 19 Jul 2012 14:43:46 +0200"
Date: Thu, 19 Jul 2012 10:52:34 -0400
Message-ID: <21289.1342709554@sss.pgh.pa.us>

Thomas Kellerer <spam_eater@gmx.net> writes:
> Lately I had some queries of the form:

>     select t.*
>     from some_table t
>     where t.id not in (select some_id from some_other_table);

> I could improve the performance of them drastically by changing the NOT NULL into an outer join:

>     select t.*
>     from some_table t
>        left join some_other_table ot on ot.id = t.id
>     where ot.id is null;

If you're using a reasonably recent version of PG, replacing the NOT IN
by a NOT EXISTS test should also help.

> Now I was wondering if a DELETE statement could be rewritten with the same "strategy":

Not at the moment.  There have been discussions of allowing the same
table name to be respecified in USING, but there are complications.

			regards, tom lane