From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: pgsql-performance@postgresql.org
To: dario_d_s@unitech.com.ar
Subject: Re: join and query planner
Date: Mon, 18 Jul 2005 15:47:34 -0500
Message-ID: <s2dbcf1d.005@gwmta.wicourts.gov> (raw)
You might want to set join_collapse_limit high, and use the JOIN
operators rather than the comma-separated lists. We generate the WHERE
clause on the fly, based on user input, and this has worked well for us.
-Kevin
>>> "Dario" <dario_d_s@unitech.com.ar> 07/18/05 2:24 PM >>>
Hi.
> Just out of curiosity, does it do any better with the following?
>
> SELECT ...
Yes, it does.
But my query could also be
SELECT ...
FROM a
JOIN b ON (a.key = b.key)
LEFT JOIN c ON (c.key = a.key)
LEFT JOIN d ON (d.key=a.key)
/*new*/ , e
WHERE (b.column <= 100)
/*new*/ and (e.key = a.key) and (e.field = 'filter')
because it's constructed by an application. I needed to know if,
somehow,
someway, I can "unforce" join order.
The only way to solve it so far is changing application. It must build
something like
SELECT ...
FROM b
JOIN (a JOIN e ON (e.key = a.key)) ON (a.key = b.key)
LEFT JOIN c ON (c.key = a.key)
LEFT JOIN d ON (d.key=a.key)
WHERE (b.column <= 100) and (e.field = 'filter')
Supossed that e.field has (should have) better selectivity. But now this
problem belongs to programmer's group :-)
The query, in fact, has more tables to join. I wonder if lowering geqo
threshold could do the work...
Thank you. Greetings. Long life, little spam and prosperity!
-----Mensaje original-----
De: pgsql-performance-owner@postgresql.org
[mailto:pgsql-performance-owner@postgresql.org]En nombre de Kevin
Grittner
Enviado el: lunes, 18 de julio de 2005 14:58
Para: pgsql-performance@postgresql.org; dariop@unitech.com.ar
Asunto: Re: [PERFORM] join and query planner
Just out of curiosity, does it do any better with the following?
SELECT ...
FROM a
JOIN b ON (a.key = b.key)
LEFT JOIN c ON (c.key = a.key)
LEFT JOIN d ON (d.key=a.key)
WHERE (b.column <= 100)
>>> snipp
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To: pgsql-performance@postgresql.org
Cc: Kevin.Grittner@wicourts.gov, dario_d_s@unitech.com.ar
Subject: Re: join and query planner
In-Reply-To: <s2dbcf1d.005@gwmta.wicourts.gov>
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