oracle 触发器“new ”，”old“的使用

1、建表 a,b 语句如下：
create table a(id number(10) not null,name varchar2(256));
create table b(id number(10) not null,name varchar2(256),update_date date,flag int );--flag 0:新增 1：修改

2、建行级触发器如下：
create or replace trigger tr_save_change
 after insert or update or delete on a
 for each row
 begin
   case when inserting then
     insert into b(id,name,update_date,flag)
     values(:new.id,:new.name,sysdate,0);
   when updating then
     update b set name=:new.name,update_date=sysdate,flag=1 where id=:old.id;
   when deleting then
     delete from b where id=:old.id;
   end case;
end;

3、测试如下：
insert into a(id,name) values(1,'aaa');
commit;
--查看b表
select * from b;

insert into a(id,name) values(2,'bbb');
commit;
--查看b表
select * from b;

update a set name='abab' where id=2;
commit;
--查看b表
select * from b;

delete from a where id=1;
commit;
--查看b表
select * from b;