From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Thomas Kellerer <spam_eater(at)gmx(dot)net> |
Cc: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: DELETE using an outer join |
Date: | 2012-07-19 14:52:34 |
Message-ID: | 21289.1342709554@sss.pgh.pa.us |
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Lists: | pgsql-sql |
Thomas Kellerer <spam_eater(at)gmx(dot)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
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