Re: unneeded joins on view - Mailing list pgsql-performance

From Heikki Linnakangas
Subject Re: unneeded joins on view
Date
Msg-id 534EA861.3020204@vmware.com
Whole thread Raw
In response to unneeded joins on view  (Linos <info@linos.es>)
Responses Re: unneeded joins on view
List pgsql-performance
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


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