Re: Altering functions cast

Hey. I used your suggestion and it worked like a
charm! The...

CREATE FUNCTION nullif_bool(text) RETURNS boolean AS '
BEGIN
RETURN nullif($1, '''');
END;
' LANGUAGE plpgsql IMMUTABLE STRICT;

THANK YOU!

--- Michael Fuhr <mike(at)fuhr(dot)org> wrote:

> On Fri, Aug 26, 2005 at 12:22:27PM -0700, Matt A.
> wrote:
> > How do I get this to work?
> >
> > create function nullif_bool(boolean) returns
> > bool as ' select nullif(''$1'','''')::bool;'
> language
> > sql;
>
> If an empty string is a possible input then the
> argument type can't
> be boolean because you'll get a syntax error before
> the function
> is called:
>
> CREATE FUNCTION nullif_bool(boolean) RETURNS boolean
> AS '
> SELECT TRUE; -- for testing
> ' LANGUAGE sql;
>
> SELECT nullif_bool('');
> ERROR: invalid input syntax for type boolean: ""
>
> The argument type should probably be text. But then
> you get a
> different error, this time during function creation:
>
> CREATE FUNCTION nullif_bool(text) RETURNS boolean AS
> '
> SELECT nullif($1,'''')::boolean;
> ' LANGUAGE sql;
> ERROR: cannot cast type text to boolean
>
> One possible solution is to use PL/pgSQL instead of
> SQL and rely
> on PL/pgSQL's automatic type conversion of the
> return value:
>
> CREATE FUNCTION nullif_bool(text) RETURNS boolean AS
> '
> BEGIN
> RETURN nullif($1, '''');
> END;
> ' LANGUAGE plpgsql IMMUTABLE STRICT;
>
> SELECT nullif_bool('');
> nullif_bool
> -------------
>
> (1 row)
>
> SELECT nullif_bool('t');
> nullif_bool
> -------------
> t
> (1 row)
>
> SELECT nullif_bool('f');
> nullif_bool
> -------------
> f
> (1 row)
>
> Is that what you're looking for?
>
> --
> Michael Fuhr
>
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