--建表语句
create table student(id number(9),name varchar2(64),age number(5));create table class(id number(9),name varchar2(64),teacherid number(9),studentid number(9));create table teacher(id number(9),name varchar2(64),age number(5)); --学生信息insert into student values(1,‘yangml‘,23);insert into student values(2,‘zhangj‘,23);insert into student values(3,‘zhulj‘,26);insert into student values(4,‘chenglp‘,26);--老师信息insert into teacher values(1,‘yangls‘,33);insert into teacher values(2,‘zhangls‘,33);insert into teacher values(3,‘zhuls‘,33);insert into teacher values(4,‘chenls‘,33);--班级信息insert into class values(1,‘一年级‘,1,1);insert into class values(2,‘二年级‘,2,2);insert into class values(3,‘三年级‘,3,3);insert into class values(4,‘四年级‘,4,4);--删除触发器create or replace trigger trigdel  before delete on class    for each rowdeclare  -- local variables herebegin   delete from teacher where teacher.id=:old.id;    delete from student where student.id=:old.id;end trigdel;--测试删除delete from class;select * from class;select * from student;select * from teacher;