Re: Cast null string '' to integer 0

Guy Rouillier wrote:

>Dwight Emmons wrote:
>
>
>>I am upgrading from Postgres 7.2 to 8.1.  We have multiple systems
>>already in place that took advantage of the implicit cast of a null
>>'' string to an integer of '0'.  It is not financially feasible for
>>us to modify all the instances.  Does anyone know of a fix?
>>
>>
>
>Well, if you want all your clients to interpret a null value in that
>column as zero, can't you just update the column to actually contain a
>zero for those rows?
>
>

I've had success for handling concatenation of null text strings (cf.
"http://www.varlena.com/varlena/GeneralBits/84.php") with

CREATE OR REPLACE FUNCTION public.textcat_null(text, text)
  RETURNS text AS
$BODY$
SELECT textcat(COALESCE($1, ''), COALESCE($2, ''));
$BODY$
  LANGUAGE 'sql' VOLATILE;
ALTER FUNCTION public.textcat_null(text, text) OWNER TO postgres;

CREATE OPERATOR public.||(
  PROCEDURE = "public.textcat_null",
  LEFTARG = text,
  RIGHTARG = text);

but for numerics I haven't been able to get a similar strategy to work
as nicely. But my suggestion would be to experiment with something to

CREATE OR REPLACE FUNCTION public.numeric_add_null("numeric", "numeric")
  RETURNS "numeric" AS
$BODY$
  SELECT numeric_add(COALESCE($1, 0), COALESCE($2, 0));
 $BODY$
  LANGUAGE 'sql' VOLATILE;

CREATE OPERATOR public.+(
  PROCEDURE = numeric_add_null,
  LEFTARG = NUMERIC,
  RIGHTARG = NUMERIC
);


It works if you can type cast:

test=# SELECT 1+NULL::NUMERIC;
 ?column?
----------
        1
(1 row)

but that may not gain you much for an existing application that you want
to avoid doing a lot of re-writing.