sub-selects

From: "Mark Fenbers" <Mark(dot)Fenbers(at)noaa(dot)gov>
To: pgsql-sql(at)postgresql(dot)org
Subject: sub-selects
Date: 2005-05-16 19:45:43
Message-ID: 4288F867.8090600@noaa.gov
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Is there a way to make a query more efficient by executing a sub-select only once?

In a query such as:

SELECT a, (select b from c where d = e limit 1), npoints( (select b from c where d = e limit 1) )

FROM f

WHERE isValid( (select b from c where d = e limit 1) );

I do the same sub-select 3 times in the query. I tried the following:

SELECT a, (select b from c where d = e limit 1) AS g, npoints( g )

FROM f

WHERE isValid( g );

But this gave an error regarding "column 'g' does not exist". How can I avoid making the same sub-select 3 times?

Mark

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