Re: one column from huge view

From: Michael Fuhr
Subject: Re: one column from huge view
Date: ,
Msg-id: 20070712125136.GA37198@winnie.fuhr.org
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In response to: Re: one column from huge view  (Heikki Linnakangas)
Responses: Re: one column from huge view  (Heikki Linnakangas)
List: pgsql-performance

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one column from huge view  (Marcin Stępnicki, )
 Re: one column from huge view  (Heikki Linnakangas, )
  Re: one column from huge view  (Michael Fuhr, )
   Re: one column from huge view  (Heikki Linnakangas, )
  Re: one column from huge view  (Tom Lane, )

On Thu, Jul 12, 2007 at 09:50:42AM +0100, Heikki Linnakangas wrote:
> Marcin Stępnicki wrote:
> >Let's say I've got a view with 100 columns and 1mln rows; some of them are
> >calculated "on the fly". For some reason I want only one column from
> >this view:
> >
> >select col1 from huge_view;
> >
> >Now, does PostgreSQL skip all the calculations from other columns and
> >executes this query faster then select * from huge_view?
>
> In simple cases, yes. But for example, if you have a LEFT OUTER JOIN in
> the view, the join is performed even if your query doesn't return any
> columns from the outer relation. Also, if the calculation contains
> immutable functions, it's not skipped.

Don't you mean "if the calculation contains VOLATILE functions,
it's not skipped"?

--
Michael Fuhr


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