Ejemplos de funciones en Mysql

DELIMITER $$
CREATE DEFINER=`root`@`localhost` 
FUNCTION `doble`(numero int) RETURNS int(11)
BEGIN

RETURN numero*2;
END$$

DELIMITER ;

DELIMITER $$
CREATE DEFINER=`root`@`localhost` FUNCTION `tipo_pelicula`
(p_film_id int) RETURNS varchar(50) CHARSET latin1
BEGIN
declare v_length int;
select length into v_length from film 
where film_id=p_film_id;

if v_length<=140 then
return 'CORTA';
else
RETURN 'LARGA';
end if;

END$$

DELIMITER ;

DELIMITER $$
USE `sakila`$$
CREATE DEFINER=`root`@`localhost` FUNCTION `factorial`(p_numero int) RETURNS int(11)
BEGIN
declare total,cont int default 1;

while cont<=p_numero do
 set total=total*cont;
 set cont=cont+1;
end while;
RETURN total;
END$$

DELIMITER ;

Uso:

select doble(8);

select title,length,tipo_pelicula(film_id) from film;

select factorial(5);