创建触发器

创建触发器，插入学生成绩时，限制必须在0-100之间。

delimiter $
create trigger t1 
before insert on sc for each row 
begin
if new.grade > 100 or new.grade < 0 then set new.grade=0;
end if;
end$

创建触发器，删除学生数据时，将删除的数据备份到数据表student_bf，以备误删除时进行数据恢复。

delimiter $$
create trigger students
before delete on student
for each row
begin
insert into student_bf select * from student
where sno=old.sno;
end;$$

创建触发器，更新员工数据时，同步更新部门表相应人数。

DELIMITER $$
CREATE TRIGGER t1
BEFORE UPDATE ON employee
FOR EACH ROW
BEGIN
UPDATE department SET emp_num=emp_num-1 WHERE dept_id=old.dept_id;
UPDATE department SET emp_num=emp_num+1 WHERE dept_id=new.dept_id;
END;$$