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Date: Wed, 25 Jan 2006 10:53:38 -0700
From: Michael Fuhr <mike@fuhr.org>
To: andrew <andrew.ylzhou@gmail.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: filtering after join
Message-ID: <20060125175338.GA76400@winnie.fuhr.org>
References: <29d3b0b90601250927o2a5ee6e6mc33a7647da4438ce@mail.gmail.com>
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On Wed, Jan 25, 2006 at 06:27:33PM +0100, andrew wrote:
> 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?

Is this what you're looking for?

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

-- 
Michael Fuhr