关于触发器的一点东西

create table STU
(
  STUNO   NUMBER(5) not null,
  STUNAME VARCHAR2(18),
  STUAGE  NUMBER(2)
)


create table UPDATE_STU
(
  STUNO   NUMBER(5),
  STUNAME VARCHAR2(18),
  STUAGE  NUMBER(2)
)


create or replace trigger before_update_stu
before update on stu
for each row
begin
insert into update_stu values(:old.stuno,:old.stuname,:old.stuage);
end;


create or replace trigger after_update_stu
after update on stu
for each row
begin
insert into update_stu values(:old.stuno,:old.stuname,:old.stuage);
end;

create or replace trigger after_insert_stu
after insert on stu
for each row
begin
insert into update_stu values(:new.stuno,:new.stuname,:new.stuage);
end;

create or replace trigger after_delete_stu
after delete on stu
for each row
begin
insert into update_stu values(:old.stuno,:old.stuname,:old.stuage);
end;