Message-ID: <534EAB01.80405@linos.es>
Date: Wed, 16 Apr 2014 18:08:33 +0200
From: Linos <info@linos.es>
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To: Heikki Linnakangas <hlinnakangas@vmware.com>,
 pgsql-performance@postgresql.org
Subject: Re: unneeded joins on view
References: <534E9E14.5000304@linos.es> <534EA861.3020204@vmware.com>
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On 16/04/14 17:57, Heikki Linnakangas wrote:
> On 04/16/2014 06:13 PM, Linos wrote:
>> I thought that Postgresql would optimize out joins on columns I
>> don't ask for when I use the view but it doesn't, this query:
> 
> It doesn't, because it would be wrong. It still has to check that the tables have a matching row (or multiple matching rows).
> 
> If you use LEFT JOINs instead, and have a unique index on all the ID columns, then the planner can do what you expected and leave out the joins.
> 
> - Heikki
> 
> 

You are right, I knew I was forgetting something important but I didn't know what was, thank you Heikki.

Regards,
Miguel Angel.


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