标题：利用Oracle触发器实现的生日年龄自动管理

假设当前用户为lsq：

create table stu1
(
sid varchar2(6) NOT NULL,
birthday timestamp
);
create table stu2
(
sid varchar2(6) NOT NULL,
age number(3)
);

insert into stu1 values('1',TO_DATE('21-4月 -1985','dd-Mon-yyyy'));
--error
insert into stu2 values('1',15);

select * from stu1;
select * from stu2;
delete from stu1;
delete from stu2;

CREATE OR REPLACE TRIGGER InsertStu1
  BEFORE INSERT ON stu1
  FOR EACH ROW
DECLARE
  v_sid varchar2(6);
  v_age number(3);
BEGIN
  v_sid:=:new.sid;
  v_age:=extract(year from sysdate)-extract(year from :new.birthday);
  insert into stu2 values(v_sid,v_age);
END InsertStu1;
/

insert into stu1 values('1',TO_DATE('21-4月 -1985','dd-Mon-yyyy'));
select * from stu1;
select * from stu2;
--error
update stu1 set birthday=TO_DATE('21-4月 -1984','dd-Mon-yyyy') where sid='1';
select * from stu1;
select * from stu2;
delete from stu1;
delete from stu2;

CREATE OR REPLACE TRIGGER UpdateStu1
  BEFORE UPDATE ON stu1
  FOR EACH ROW
DECLARE
  v_sid varchar2(6);
  v_age number(3);
BEGIN
  v_sid:=:old.sid;
  v_age:=extract(year from sysdate)-extract(year from :new.birthday);
  update stu2 set age=v_age where sid=v_sid;
END UpdateStu1;
/

insert into stu1 values('1',TO_DATE('21-4月 -1985','dd-Mon-yyyy'));
select * from stu1;
select * from stu2;
update stu1 set birthday=TO_DATE('21-4月 -1984','dd-Mon-yyyy') where sid='1';
select * from stu1;
select * from stu2;
--error
delete from stu1 where sid='1';
select * from stu1;
select * from stu2;
delete from stu1;
delete from stu2;

CREATE OR REPLACE TRIGGER DeleteStu1
  BEFORE delete ON stu1
  FOR EACH ROW
DECLARE
  v_sid varchar2(6);
BEGIN
  v_sid:=:old.sid;
  delete stu2 where sid=v_sid;
END DeleteStu1;
/

insert into stu1 values('1',TO_DATE('21-4月 -1985','dd-Mon-yyyy'));
select * from stu1;
select * from stu2;
delete from stu1 where sid='1';
delete from stu1;
delete from stu2;

更好的处理方案，使得用户不可能对不应该直接操纵的表进行操作
Connect system/sys@orcl;
create user newuser identified by newuser;
grant select on lsq.stu1 to newuser;
grant select on lsq.stu2 to newuser;
grant connect to newuser;
grant update,insert,delete on lsq.stu1 to newuser;

Connect newuser/newuser@orcl;
select * from lsq.stu1;
insert into lsq.stu1 values('1',TO_DATE('21-4月 -1985','dd-Mon-yyyy'));
select * from lsq.stu1;
select * from lsq.stu2;
update lsq.stu1 set birthday=TO_DATE('21-4月 -1984','dd-Mon-yyyy') where sid='1';
select * from lsq.stu1;
select * from lsq.stu2;
delete from lsq.stu1 where sid='1';
select * from lsq.stu1;
select * from lsq.stu2;

--error
insert into lsq.stu2 values('1',24);
update lsq.stu2 set age=22 where sid='1';