MySQL: Разбиение текста на токены

DELIMITER ;;

CREATE DEFINER=`root`@`localhost`
FUNCTION `StrTok`(
    `in_string` VARCHAR(255),
    `delims` VARCHAR(255),
    `str_replace` VARCHAR(255))
RETURNS varchar(255) CHARSET utf8
    NO SQL
    DETERMINISTIC
BEGIN
    DECLARE str_len, delim_len, a, b, is_delim INT;
    DECLARE z, y VARBINARY(1);
    DECLARE str_out VARBINARY(256);
    SET str_len = CHAR_LENGTH(in_string);
    SET delim_len = CHAR_LENGTH(delims);
    SET a = 1, b = 1, is_delim = 0, str_out = '';

    WHILE a <= str_len DO
        SET z = SUBSTRING(in_string, a, 1);

        WHILE b <= delim_len AND is_delim < 1 DO
            SET y = SUBSTRING(delims, b, 1);

            IF z = y THEN
                SET is_delim = 1;
            END IF;
            SET b = b + 1;
        END WHILE;

        IF is_delim = 1 THEN
            SET str_out = CONCAT(str_out, str_replace);
        ELSE
            SET str_out = CONCAT(str_out, z);
        END IF;

        SET b = 0;
        SET is_delim = 0;
        SET a = a + 1;
    END WHILE;
    RETURN str_out;
END ;;

DELIMITER ;