Посчитать длину подстроки в строке

DELIMITER @@;
CREATE FUNCTION CountZeroes (inString TEXT)
RETURNS INT 
DETERMINISTIC 
NO SQL 
BEGIN
DECLARE counter INT DEFAULT 0;
DECLARE temp INT DEFAULT 0;
SET inString = COALESCE(inString, '');
WHILE inString != '' DO
        IF LEFT(inString, 1) = '0' THEN SET temp = temp + 1;
        ELSE
                SET counter = GREATEST(counter, temp);
                SET temp = 0;
        END IF;
        SET inString = SUBSTRING(inString FROM 2);
END WHILE;
RETURN GREATEST(counter, temp);
END;
@@;
DELIMITER ;

И потом

SELECT CountZeroes("0000---111---222000001234567890")
     , CountZeroes("0012345678900001");