From: | Mike Mascari <mascarm(at)mascari(dot)com> |
---|---|
To: | Abdul-wahid Paterson <aw(at)lintrix(dot)net> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: query optimisation |
Date: | 2003-03-15 01:18:24 |
Message-ID: | 3E727F60.9090506@mascari.com |
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Thread: | |
Lists: | pgsql-general |
Abdul-wahid Paterson wrote:
> Hi,
>
> I have a query of the form:
>
> select a.id, e.id from tablea a, tableb b, tablec c, tabled d, tablee e
> where a.fk=b.id and b.fk=c.id and c.fk=d.id and d.fk=e.id;
>
> In fact, my statement is a bit more complex as it is joined across 7
> tables, has an aggregate function and a CASE statement.
>
> My problem is that it executes to slow and I need to optimise it. Is
> there any documentation anywhere that can help me work out how to
> optimise the statement? My statement has a few other conditions that
> need to be met on the joining tables. Does changing the order of the
> conditional statement affect the way the statement is optimised?
Assuming indexes on the appropriate tables and a recent VACUUM
ANALYZE, I've found that using explicit joins can reduce
planning time significantly:
http://www.postgresql.org/docs/view.php?version=7.2&idoc=0&file=explicit-joins.html
Hope that helps,
Mike Mascari
mascarm(at)mascari(dot)com
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