procedure problem, returns null

[next]

Procedure:

DELIMITER $$

DROP PROCEDURE IF EXISTS `test`.`discounted_price` $$
CREATE DEFINER=`root`@`localhost` PROCEDURE `discounted_price`(price NUMERIC(8, 2), OUT discount_price NUMERIC(8, 2))
BEGIN

  IF(price > 500) THEN
    SET discount_price = price * 0.8;
  ELSEIF(price > 100) THEN
    SET discount_price = price * 0.9;
  ELSE
    SET DISCOUNT_price = price;
  END IF;

END $$

DELIMITER ;

 

call:

CALL discounted_price(300, @new_price);
SELECT @new_price;

 

this should return price after discount, but for some reason returns 'null'. How do i fix this?

Also what does '@' do?

 

Thanks.