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Include result of function call within WHERE clause in results

From: Dallas Morisette <p28flyer(at)gmail(dot)com>
To: pgsql-novice(at)postgresql(dot)org
Subject: Include result of function call within WHERE clause in results
Date: 2009-05-17 00:44:42
Message-ID: 1717FB3A-2E7F-4CD4-B15D-5DC24D0A28FD@gmail.com (view raw or flat)
Thread:
Lists: pgsql-novice
Hi all -

I need to select the rows of a table that satisfy a condition that  
includes a function call, and I want to include the result of the  
function call as a column in the resulting table. For example, this  
pseudo-code produces the result I'm looking for:

SELECT field1, some_function(...) FROM my_table
WHERE some_function(...) < some_number

However, I would like to avoid calling the function in two places,  
especially since embedded in the parameters to the function I have  
another SELECT command. Not to mention it just looks messy...

I've already tried the following without luck:

SELECT field1, some_function(...) AS result FROM my_table
WHERE result < some_number

Is there a way to cache the result of the function call so it can be  
used in both places without two separate calls?

Thanks in advance,
Dallas Morisette

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Subject: COUNT() BASED ON MULTIPLE WHERE CONDITIONS
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