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To: "Marc G. Fournier" <scrappy@postgresql.org>
Cc: pgsql-sql@postgresql.org
Subject: Re: [HACKERS] ALTER TABLE ( smallinto -> boolean ) ... 
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Comments: In-reply-to "Marc G. Fournier" <scrappy@postgresql.org>
	message dated "Thu, 01 Sep 2005 18:15:25 -0300"
Date: Thu, 01 Sep 2005 17:25:28 -0400
Message-ID: <6752.1125609928@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Marc G. Fournier" <scrappy@postgresql.org> writes:
> all I want to do is:

> CREATE CAST ( 0 AS boolean )
>         WITH FUNCTION <I have to create this>
>           AS ASSIGNMENT;

> And then each time I try to insert a '0' into a BOOLEAN field, it will 
> auto convert that (based on my function) to 'f' ...

> And I'd need to do a second one for 1 -> 't' ...

No, you want one function from smallint to boolean, and the cast the
same way.  (The cast is really just syntactic sugar for invoking the
function.)

Depending on what you want this to do, you might have to make the cast
IMPLICIT rather than ASSIGNMENT.  I'd try ASSIGNMENT first, though,
since it's less likely to bite you when you weren't expecting it.

			regards, tom lane