DELIMITER //
DROP FUNCTION IF EXISTS uniqueChars//

CREATE FUNCTION uniqueChars(s TEXT) RETURNS TEXT
DETERMINISTIC
BEGIN
        DECLARE output TEXT DEFAULT '';
        DECLARE temp CHAR(1);

        WHILE s <> ''  DO
                SET temp = SUBSTR(s FROM 1 FOR 1);
                IF NOT LOCATE(temp, output) THEN
                        SET output = CONCAT(output, temp);
                END IF;
                SET s = SUBSTR(s FROM 2);
        END WHILE;
        RETURN output;
END//

DELIMITER ;