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Re: WITH AS vs subselect was: count (DISTINCT expression[ , ... ] ) and documentation

From: David Fetter <david(at)fetter(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it>,pgsql-general(at)postgresql(dot)org
Subject: Re: WITH AS vs subselect was: count (DISTINCT expression[ , ... ] ) and documentation
Date: 2008-12-27 07:10:43
Message-ID: 20081227071043.GC3793@fetter.org (view raw or flat)
Thread:
Lists: pgsql-general
On Fri, Dec 26, 2008 at 07:13:48PM -0500, Tom Lane wrote:
> Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it> writes:
> >>> David Fetter <david(at)fetter(dot)org> wrote:
> >>>> In 8.4, you'll be able to do:
> 
> >>>> WITH d AS (
> >>>> SELECT DISTINCT c1, c2 FROM table1
> >>>> )
> >>>> SELECT count(*) FROM d;
> 
> >>> Nice, but what will be the difference from
> >>> select count(*) from (select distinct c1, c2 from t);
> >>> ?
> >>> Optimisation?
> 
> >> None especially.
> 
> > So what would be the advantage compared to subselect?
> 
> None, David just has WITH on the brain ;-)

LOL!

You're only saying that because it's true ;)

Cheers,
David.
-- 
David Fetter <david(at)fetter(dot)org> http://fetter.org/
Phone: +1 415 235 3778  AIM: dfetter666  Yahoo!: dfetter
Skype: davidfetter      XMPP: david(dot)fetter(at)gmail(dot)com

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