How can I convert this Postgres stored procedure to MYSQL

[Jon Bowlas]

I'm pretty new to db development but I have a requirement to create a entry versioning database, I found this postgres example of how this can be achieved easliy but I dont know how to convert to MYSQL (we're running MySQL 4.0.16) so could somebody please help me to convert it:

CREATE FUNCTION func_table1_vc ()
RETURNS OPAQUE AS '
DECLARE
v integer;
BEGIN
SELECT INTO v version FROM shadow_table1
WHERE id = OLD.id
ORDER BY version DESC LIMIT 1;
IF v ISNULL THEN
v := 0;
ELSE
v := v + 1;
END IF;
INSERT INTO shadow_table1
VALUES (OLD.id,OLD.data1,OLD.data2,v);
RETURN NEW;
END;
' LANGUAGE 'plpgsql';

Hope someone can help

Jon