级联删除 
ON DELETE CASCADE 

-- 重新创建添加级联操作
CREATE TABLE employee(
     eid INT PRIMARY KEY AUTO_INCREMENT,
     ename VARCHAR(20),
     age INT,
     dept_id INT, 
     CONSTRAINT emp_dept_fk FOREIGN KEY(dept_id) REFERENCES department(id)，
     -- 添加级联删除
     ON DELETE CASCADE 
);

-- 添加数据
INSERT INTO employee (ename, age, dept_id) VALUES (‘张百万‘, 20, 1); 
INSERT INTO employee (ename, age, dept_id) VALUES (‘赵四‘, 21, 1); 
INSERT INTO employee (ename, age, dept_id) VALUES (‘广坤‘, 20, 1);
INSERT INTO employee (ename, age, dept_id) VALUES (‘小斌‘, 20, 2); 
INSERT INTO employee (ename, age, dept_id) VALUES (‘艳秋‘, 22, 2); 
INSERT INTO employee (ename, age, dept_id) VALUES (‘大玲子‘, 18, 2); 

-- 删除部门编号为2 的记录 
DELETE FROM department WHERE id = 2;