filtering after join

From: andrew <andrew(dot)ylzhou(at)gmail(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: filtering after join
Date: 2006-01-25 17:49:29
Message-ID: 29d3b0b90601250949t1991b0f9l6026405b80e9dc28@mail.gmail.com
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I want to use a UDF to filter tuples t that are generated after a join.
More specifially, I have a UDF foo(record), which computes a value for
a given tuple. I can do the filtering before the join. e.g.:

select * from A, B where foo(A)<2 and A.a=B.b;

But I want to apply foo() to the tuples generated by the join
operation. How can I do that?
Thanks!
--
andrew

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