Altering functions cast

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

We use NULLIF() for adding [1|0|null] according to the
evalution of nullif('x','') into boolean columns.
Where x is [1|0|null], which if it's an empty string
(x='') then we add NULL cause NULLIF says if '' == ''
then return NULL into boolean.

An example wrapper function for this with an integer
cast:

CREATE FUNCTION nullif_always_int(text) RETURNS
integer AS '
SELECT nullif($1,'''')::int;
' LANGUAGE SQL;

I was hoping I could do something simliar with
booleans if possible?

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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@fuhr.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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