Message-ID: <4317713C.10808@dunslane.net>
Date: Thu, 01 Sep 2005 17:23:08 -0400
From: Andrew Dunstan <andrew@dunslane.net>
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: "Marc G. Fournier" <scrappy@postgresql.org>, pgsql-hackers@postgresql.org
Subject: Re: ALTER TABLE ( smallinto -> boolean ) ...
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	<6399.1125608205@sss.pgh.pa.us>
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Tom Lane wrote:

>"Marc G. Fournier" <scrappy@postgresql.org> writes:
>  
>
>>On Mon, 29 Aug 2005, Tom Lane wrote:
>>    
>>
>>>No, because there's no built-in cast from smallint to bool.
>>>      
>>>
>
>  
>
>>'k, I just took a read through the "CREATE CAST" man page, and don't think 
>>I can use that for this,
>>    
>>
>
>Sure you can.  Make a SQL or PLPGSQL function that does the conversion
>you want and then create a cast using it.
>  
>

That probably won't help him much with "values(0)":

andrew=# create function ibool(smallint) returns boolean language sql as 
$$ select $1 <> 0 $$;
CREATE FUNCTION
andrew=# create cast (smallint as boolean) with function ibool(smallint) 
as implicit;
CREATE CAST
andrew=# insert into foobool values(0);
ERROR:  column "x" is of type boolean but expression is of type integer
HINT:  You will need to rewrite or cast the expression.

Is there a way to make the builtin int to bool cast implicit?

cheers


andrew