mysql创建触发器报错，请高手帮忙看下

DROP TABLE if EXISTS tb;
CREATE TABLE tb(BH CHAR(16),content VARCHAR(20),date DATETIME,val INT);

CREATE TRIGGER tri_NewBH BEFORE INSERT ON tb
FOR EACH ROW
BEGIN
DECLARE dt CHAR(8)
DECLARE bh_id CHAR(16)
DECLARE number INT(1)
DECLARE new_bh VARCHAR(16)

     SET dt = DATE_FORMAT(CURDATE(),'%Y%m%d')     SELECT         MAX(BH) INTO bh_id     FROM tb     WHERE BH LIKE CONCAT(dt,'%')     IF bh_id = '' OR bh_id IS NULL THEN         SET new_bh = CONCAT(dt,'00000001')     ELSE        SET number = RIGHT(bh_id,8) + 1        SET new_bh =  RIGHT(CONCAT('00000000',number),8)        SET new_bh=CONCAT(dt,new_bh)     END IF     SET NEW.BH = new_bh END