trigger instead of 事件觸發 用戶和系統

定義：instead of

      1) 基於view表單的處理可以在表和視圖上指定一個instead of 觸發器

      2) 執行這種觸發器可以代替原來的觸發器,instead of 觸發器擴展了視圖跟新類型

      3) 每一個表和視圖只能有一個instead of 觸發器

      4) INSTEAD OF觸發器被用於更新那些沒有辦法通過正常方式更新的視圖

      5) INSTEAD OF觸發器的主要優點就是可以使不能更新的視圖支持更新。基於多個表的視圖必須使用。

      6) INSTEAD OF觸發器來支持多個表中數據的插入、更新和刪除操作。
      注：不能在帶有with check option 定義的視圖中創建INSTEAD OF觸發器

 

第一：instead of 觸發器：

a: 有關insert的觸發時間的觸發器

--step 1 create referenced table

create table stu(
stu_id number(9) primary key,
stu_name varchar2(25)
)

create table course(
c_id number(9) primary key,
grade varchar2(25),
foreign key (c_id) references stu(stu_id)
)

create table stu(
stu_id number(9) primary key,
stu_name varchar2(25)
)

create table course(
c_id number(9) primary key,
grade varchar2(25),
foreign key (c_id) references stu(stu_id)
)

 --step 2 create a view

create view sc_view as
select stu.stu_id,stu.stu_name,course.grade from stu,course where stu.stu_id=course.c_id

create view sc_view as 
select stu.stu_id,stu.stu_name,course.grade from stu,course where stu.stu_id=course.c_id

測試：testing insert one statement

insert into sc_view values(5,'lily','75');

insert into sc_view values(5,'lily','75');

結果：result:

 

 --step3  create a trigger

create or replace trigger tri_sc_view
instead of insert on sc_view
begin
insert into stu values(:new.stu_id,:new.stu_name);
insert into course values(:new.stu_id,:new.grade);
end;

create or replace trigger tri_sc_view
instead of insert on sc_view
begin
insert into stu values(:new.stu_id,:new.stu_name);
insert into course values(:new.stu_id,:new.grade);
end;

 提示：很多人糾結爲什麼 插入 stu & course表中的：new.stu_id是一樣了？其實new.stu_id只是一個數值而已，那這句語句分析insert into sc_view values(5,'lily','75'); ：new.new.stu_id 就是5，：new.stu_name就是‘lily’，：new.grade就是‘75’。他們的產生是根據創建的視圖表sc_view的到的。觸發器的執行過程是，先遇到觸發事件這裏指：insert into sc_view values(5,'lily','75'); 然後產生想對應的：new.stu_id ，：new.stu_name，：new.grade。將這些值賦值給了觸發器作用的表單； 

 

執行語句：

1)

insert into sc_view values(1,'justin','88');
insert into sc_view values(2,'irs','70');
insert into sc_view values(3,'danile,'90);
insert into sc_view values(4,'tina,'75');
insert into sc_view values(5,'lily','75');

insert into sc_view values(1,'justin','88');
insert into sc_view values(2,'irs','70');
insert into sc_view values(3,'danile,'90);
insert into sc_view values(4,'tina,'75');
insert into sc_view values(5,'lily','75');

 結果：

select * from sc_view

select * from sc_view

 

  

select * from stu

select * from stu

 

 

select * from course

select * from course

 

 

創建了view的trigger以後，可以直接通過添加wiew表單的數據來實現其他關聯表的處理。。

 

2）

insert into stu values(6,'eric');

insert into stu values(6,'eric');

 

insert into course values(6,'95');

insert into course values(6,'95');

 

結果：

 

實際上是一起跟新的...

 

b)有關更新update的觸發器；

select * from employees

create sequence empl_seq;

alter table employees drop(job_id,manger_id,department_id,dn)

insert into employees values(empl_seq.nextval,'daniel','hwong','[email protected]','15902701688',sysdate,2000,.12);

insert into employees values(empl_seq.nextval,'justin','williams','[email protected]','15902701114',sysdate,5000,.12);

create or replace view tt_view as
select employees.first_name||','||employees.last_name v_name,employees.email,employees.phone_no,employees.employee_id from employees

select * from tt_view

update tt_view set v_name='justin2,william2'where employee_id=2
--執行彈出 oracl-01733此處不允許修改虛擬值--

create or replace trigger tri_employ
instead of update on tt_view
begin
update employees set
                     employees.first_name=substr(:new.v_name,instr(:new.v_name,',')+1),
                     employees.last_name=substr(:new.v_name,1,instr(:new.v_name,',')-1),
                     employees.phone_no=:new.phone_no,
                     employees.email=:new.email
                     where employees.employee_id=:new.employee_id;
end;

select * from employees

create sequence empl_seq;

alter table employees drop(job_id,manger_id,department_id,dn)

insert into employees values(empl_seq.nextval,'daniel','hwong','[email protected]','15902701688',sysdate,2000,.12);

insert into employees values(empl_seq.nextval,'justin','williams','[email protected]','15902701114',sysdate,5000,.12);

create or replace view tt_view as
select employees.first_name||','||employees.last_name v_name,employees.email,employees.phone_no,employees.employee_id from employees

select * from tt_view

update tt_view set v_name='justin2,william2'where employee_id=2
--執行彈出 oracl-01733此處不允許修改虛擬值--

create or replace trigger tri_employ
instead of update on tt_view
begin
update employees set 
                     employees.first_name=substr(:new.v_name,instr(:new.v_name,',')+1),
                     employees.last_name=substr(:new.v_name,1,instr(:new.v_name,',')-1),
                     employees.phone_no=:new.phone_no,
                     employees.email=:new.email
                     where employees.employee_id=:new.employee_id;
end;

第二：用戶事件觸發器；

create trigger ad_startup
 after startup
  on database
begin
 -- do some stuff
end;

create trigger ad_startup
 after startup
  on database
begin
 -- do some stuff
end;

 第三:系統觸發器；

-----用戶事件：用戶登陸、註銷，CREATE / ALTER / DROP / ANALYZE / AUDIT / GRANT / REVOKE /
RENAME / TRUNCATE / LOGOFF

 

create table droped_objects(
 object_name varchar2(30),
 object_type varchar2(30),
 dropped_on date);

create table droped_objects(
 object_name varchar2(30),
 object_type varchar2(30),
 dropped_on date);

 

create or replace trigger log_drop_trigger
 before drop on donny.schema
begin
 insert into droped_objects values(
  ora_dict_obj_name,  -- 與觸發器相關的函數
  ora_dict_obj_type,
  sysdate);
end;

create or replace trigger log_drop_trigger
 before drop on donny.schema
begin
 insert into droped_objects values(
  ora_dict_obj_name,  -- 與觸發器相關的函數
  ora_dict_obj_type,
  sysdate);
end;

 

create table drop_me(a number);
create view drop_me_view as select *from drop_me;
drop view drop_me_view;
drop table drop_me;
select *from droped_objects

create table drop_me(a number);
create view drop_me_view as select *from drop_me;
drop view drop_me_view;
drop table drop_me;
select *from droped_objects

 

禁用和啓用觸發器
alter trigger <trigger_name> disable;
alter trigger <trigger_name> enable;
事務處理：
在觸發器中，不能使用commit / rollback
因爲ddl語句具有隱式的commit，所以也不允許使用