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From: "Phillip Smith" <phillip.smith@weatherbeeta.com.au>
To: "'Stuart McGraw'" <smcg2297@frii.com>,
	<pgsql-sql@postgresql.org>
Subject: Re: slowness when subselect uses DISTINCT
Date: Thu, 19 Apr 2007 08:43:49 +1000
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May I suggest you post an EXPLAIN ANALYZE to the group for the query =
you're
having problems with...?


-----Original Message-----
From: pgsql-sql-owner@postgresql.org =
[mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of Stuart McGraw
Sent: Thursday, 19 April 2007 04:17
To: pgsql-sql@postgresql.org
Subject: [SQL] slowness when subselect uses DISTINCT

I have several times now run into what seems
like similar performance problems with some=20
of my postgresql queries.

I have a view that runs reasonably quicky.

I use this view in a subselect in another=20
query and that query too runs reasonably
quicky.

The view returns some unwanted duplicate=20
rows so I modify it using either DISTINCT=20
or GROUP BY to eliminate them.
View still runs reasonably quickly.

I use the modified view as a subselect as
above, but now the query runs 2-3 orders
of magnitude more slowly than before.

Before I go through the effort of putting=20
together a specific and concise test case,=20
has anyone seen this general pattern and=20
have an explanation or advice?  (PG-8.2.3)


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