SQL 触发器：限制商品表更新操作

CREATE TRIGGER TRI_商品 BEFORE UPDATE ON 商品 FOR EACH ROW BEGIN DECLARE shop_count INT; SELECT COUNT(*) INTO shop_count FROM 商店 WHERE 商店编号 = NEW.商店编号; IF shop_count > 0 THEN SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = '不能更新商品信息，该商店编号已存在'; END IF; END;