MySQL stored procedure to generate EAN8

gistfile1.txt

CREATE DEFINER=`root`@`%` FUNCTION `GEN_EAN8`(
	`CODE` INT

)
RETURNS vARCHAR(8)
LANGUAGE SQL
NOT DETERMINISTIC
NO SQL
SQL SECURITY DEFINER
COMMENT ''
BEGIN
	DECLARE response VARCHAR(8);
	DECLARE prefix CHAR(1);
	DECLARE indx INT;
	DECLARE SumODD INT;
	DECLARE SumEven INT;
	DECLARE Summ INT;
	SET prefix = '2';
	
	SET response = CAST(CODE as varchar(8));
	
	WHILE LENGTH(response)<7-LENGTH(prefix) DO
		SET response = CONCAT('0',response);
	END WHILE;
	
	SET response = CONCAT(prefix,response);
	
	SET indx = LENGTH(response);
	SET SumODD = 0;
	SET SumEven = 0;
	WHILE indx > 2 DO
		SET SumODD = SumODD+CAST(SUBSTRING(response,indx,1) AS INT);
		SET indx = indx-1;
		SET SumEven = SumEven+CAST(SUBSTRING(response,indx,1) AS INT);
		SET indx = indx-1;
	END WHILE;
	SET SumODD = SumODD+CAST(SUBSTRING(response,indx,1) AS INT);
	
	SET Summ = SumODD * 3 + SumEven;
	SET indx = CASE Summ % 10
            WHEN 0 THEN '0'
            ELSE 10 - Summ % 10
        END;
	SET response = CONCAT(response,CAST(indx AS VARCHAR(1)));
	RETURN(response);
END