[Taleason]

Try this

DROP FUNCTION IF EXISTS `GetMobTypeById`;
DELIMITER ;;
CREATE DEFINER=`root`@`localhost` FUNCTION `GetMobTypeById`(mobid INTEGER UNSIGNED) RETURNS char(1) CHARSET latin1
BEGIN
    DECLARE Result CHAR(1);

    SET Result = NULL;

    IF (select id from character_ where id = mobid) > 0 THEN
      SET Result = 'C';
    ELSEIF (select BotID from bots where BotID = mobid) > 0 THEN
      SET Result = 'B';
    END IF;

    RETURN Result;
END;;
DELIMITER ;