From Mark.Fenbers@noaa.gov Mon May  16 19:45:57 2005
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Message-ID: <4288F867.8090600@noaa.gov>
Date: Mon, 16 May 2005 15:45:43 -0400
From: "Mark Fenbers" <Mark.Fenbers@noaa.gov>
Organization: DoC/NOAA/NWS/OHRFC
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To: pgsql-sql@postgresql.org
Subject: sub-selects
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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Is there a way to make a query more efficient by executing a sub-select
only once?<br>
<br>
In a query such as:<br>
<br>
<tt>SELECT a, (select b from c where d = e limit 1), npoints( (select b
from c where d = e limit 1) )<br>
&nbsp;&nbsp;&nbsp; FROM f<br>
&nbsp;&nbsp;&nbsp; WHERE isValid( (select b from c where d = e limit 1) );<br>
</tt><br>
I do the same sub-select 3 times in the query.&nbsp; I tried the following:<br>
<br>
<tt>SELECT a, (select b from c where d = e limit 1)<b> AS g</b>,
npoints( <b>g</b> )<br>
&nbsp;&nbsp;&nbsp; FROM f<br>
&nbsp;&nbsp;&nbsp; WHERE isValid( <b>g</b> );<br>
</tt><br>
But this gave an error regarding "column 'g' does not exist".&nbsp; How can
I avoid making the same sub-select 3 times? <br>
<br>
Mark<br>
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From lists@boutiquenumerique.com Mon May  16 20:36:04 2005
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To: "Mark Fenbers" <Mark.Fenbers@noaa.gov>, pgsql-sql@postgresql.org
Subject: Re: sub-selects
References: <4288F867.8090600@noaa.gov>
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Date: Mon, 16 May 2005 22:36:01 +0200
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SELECT foo.*,  npoints( foo.g )
FROM
(SELECT a, (select b from c where d = e limit 1) AS g FROM f WHERE  
isValid( g ))
AS foo

?