SQL触发器实例(上)

--1.) 创建测试用的表(testTable)
if exists (select * from sysobjects where name='testTable')
drop table testTable
GO
Create Table testTable
(
testField varchar(50)
)

 select * from testTable



--2.) 创建基于表(testTable)的触发器(testTrigger)
IF EXISTS (Select name FROM sysobjects Where name = 'testTrigger' AND type = 'TR')
Drop TRIGGER testTrigger
GO
Create Trigger testTrigger 
ON testTable 
for Insert,Delete,Update
AS
if exists(select * from inserted)
     if exists(select * from deleted)
         print '...更新'
     else
         print '...插入'
else
     if exists(select * from deleted)
         print '...删除'
Go


--.) 操作testTable表,测试触发器testTrigger
--分别执行Insert Into语句,Update语句,Delete语句,看看效果
Insert Into testTable values ('testContent!')

Update testTable Set testField = 'UpdateContent'

Delete From testTable

select * from testTable


--用到的功能有: 
        --1.如果我更改了学生的学号,我希望他的借书记录仍然与这个学生相关(也就是同时更改借书记录表的学号); 
        --2.如果该学生已经毕业，我希望删除他的学号的同时，也删除它的借书记录，等等。

 --这时候可以用到触发器。对于需求1，创建一个Update触发器： 

     Create Trigger truStudent 

       On student      --在Student表中创建触发器 
       instead of Update      --为什么事件触发 
     As           --事件触发后所要做的事情 
       if Update(stuID)            
       begin 

         Update borrow 
           Set stuID=i.stuID 
           From borrow as br , Deleted as d ,Inserted as i      --Deleted和Inserted临时表 
           Where br.stuID=d.stuID 

       end   

drop trigger truStudent
UPDATE student set stuID='1006' WHERE stuID='1005'


    Create trigger trdStudent
       On Student 
       instead of Delete 
     As 
     Delete Borrow 
　　　From Borrow as br , Deleted as d Where br.StuID=d.stuID 

drop trigger trdStudent
delete FROM student WHERE stuID='1004'

disable trigger trdStudent on Student

select * from book
select * from borrow
select * from student


--创建触发器（对删除表的约束）
create trigger droptabel
on database
for drop_table
as
print'删除表吗？'
print'不能删除表'
rollback transaction
go

drop table students
disable trigger droptabel on database　　　　--关闭触发器
enable trigger droptabel on database





CREATE TABLE students  --学生信息表
(
  stuID CHAR(10) primary key,  --学生编号
  stuName  CHAR(10) NOT NULL ,     --学生名称
  major  CHAR(50) NOT NULL    --专业
)
GO


CREATE TABLE borrowS  --借书表
(
 borrowID  CHAR(10) primary key,    --借书编号
stuID CHAR(10) NOT NULL, --学生编号
BID  CHAR(10) NOT NULL,--图书编号
 T_time  datetime NOT NULL,   --借出日期
 B_time  datetime    --归还日期
)
GO

SElect * from students
select * from borrows

Create Trigger truStudents 

       On students      --在Student表中创建触发器 
       for Update      --为什么事件触发 
     As           --事件触发后所要做的事情 
       if Update(stuID)            
       begin 

         Update borrows 
           Set stuID=i.stuID 
           From borrows as br , Deleted as d ,Inserted as i      --Deleted和Inserted临时表 
           Where br.stuID=d.stuID 

       end   



UPDATE studentS set stuID='1006' WHERE stuID='1005'


    Create trigger trStudent
       On Students 
       for Delete 
     As 
       Delete borrows 
         From borrows AS br , Deleted AS d 
         Where br.stuID=d.stuID 


drop trigger trStudent


delete from students where stuID='1001'