触发器例题

题1：建一个触发器addstudent_trigger, 当用户向Student表中插入一条新的记录时，更新该班级的学生人数。可先创建一个班级表用于统计学生人数。 create trigger addstudent_trigger after insert on Student begin declare c int; set c = (select stuCount from class); update class set stuCount = c + 1; end;

题2 创建一个触发器delstudent_ trigger，当删除一条学生记录时，把这个学生所有的选课记录都删除掉。

create trigger delstudent_ trigger before delete on Student begin delete from class_choose where(select class.choose.stuid = student.id); end;

题3 创建一个触发器delstudent_new_trigger，当删除学生记录时，先检查有没有他的选课记录，若还有选课记录的话不允许删除改学生；如果没有选课记录了允许删除。

create trigger delstudent_new_trigger before delete on Student

If((select * from class_choose where class_choose.stuid = student.id)>0) begin delete from class_choose where(select class.choose.stuid = student.id); end; else begin commit transaction end;