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Thread: Altering functions cast

Altering functions cast

From
"Matt A."
Date:
How do I get this to work?

create function nullif_bool(boolean) returns
bool as ' select nullif(''$1'','''')::bool;' language
sql;

???

Thank you.





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Re: Altering functions cast

From
Michael Fuhr
Date:
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

Altering functions cast

From
"Matt A."
Date:
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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Re: Altering functions cast

From
"Matt A."
Date:
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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