我在mysql中编写了一个小的触发器函数。这是我编写的触发器查询，并在代码中给出语法错误。
错误：
sql语法有错误；查看与mysql服务器版本对应的手册，以获得使用“cp where”附近的正确语法 cp . customer_plan_id =第一个id；

DELIMITER $$
CREATE TRIGGER delete_plan_on_delete_customer 
    AFTER DELETE ON customers
    FOR EACH ROW 
BEGIN
    DECLARE active_plan INT;
    DECLARE first_id INT;

    SET active_plan = (SELECT is_active
    FROM customer_plans 
    WHERE customer_id=OLD.customer_id AND first_plan_id=1);

    if(active_plan = 0)THEN

        SET first_id = (SELECT customer_plan_id
        FROM customer_plans 
        WHERE customer_id=OLD.customer_id AND first_plan_id=1);

        DELETE customer_plans cp WHERE `cp`.`customer_plan_id`= first_id;
   END IF; 
END$$
DELIMITER ;