程序師世界是廣大編程愛好者互助、分享、學習的平台,程序師世界有你更精彩!
首頁
編程語言
C語言|JAVA編程
Python編程
網頁編程
ASP編程|PHP編程
JSP編程
數據庫知識
MYSQL數據庫|SqlServer數據庫
Oracle數據庫|DB2數據庫
 程式師世界 >> 數據庫知識 >> 其他數據庫知識 >> 更多數據庫知識 >> 深入淺析SQL Server 觸發器,淺析sql

深入淺析SQL Server 觸發器,淺析sql

編輯:更多數據庫知識

深入淺析SQL Server 觸發器,淺析sql


觸發器是一種特殊類型的存儲過程,它不同於之前的我們介紹的存儲過程。觸發器主要是通過事件進行觸發被自動調用執行的。而存儲過程可以通過存儲過程的名稱被調用。

Ø 什麼是觸發器

    觸發器對表進行插入、更新、刪除的時候會自動執行的特殊存儲過程。觸發器一般用在check約束更加復雜的約束上面。觸發器和普通的存儲過程的區別是:觸發器是當對某一個表進行操作。諸如:update、insert、delete這些操作的時候,系統會自動調用執行該表上對應的觸發器。SQL Server 2005中觸發器可以分為兩類:DML觸發器和DDL觸發器,其中DDL觸發器它們會影響多種數據定義語言語句而激發,這些語句有create、alter、drop語句。

    DML觸發器分為:

    1、 after觸發器(之後觸發)
        a、 insert觸發器
        b、 update觸發器
        c、 delete觸發器
    2、 instead of 觸發器 (之前觸發)

    其中after觸發器要求只有執行某一操作insert、update、delete之後觸發器才被觸發,且只能定義在表上。而instead of觸發器表示並不執行其定義的操作(insert、update、delete)而僅是執行觸發器本身。既可以在表上定義instead of觸發器,也可以在視圖上定義。

    觸發器有兩個特殊的表:插入表(instered表)和刪除表(deleted表)。這兩張是邏輯表也是虛表。有系統在內存中創建者兩張表,不會存儲在數據庫中。而且兩張表的都是只讀的,只能讀取數據而不能修改數據。這兩張表的結果總是與被改觸發器應用的表的結構相同。當觸發器完成工作後,這兩張表就會被刪除。Inserted表的數據是插入或是修改後的數據,而deleted表的數據是更新前的或是刪除的數據。

    Update數據的時候就是先刪除表記錄,然後增加一條記錄。這樣在inserted和deleted表就都有update後的數據記錄了。注意的是:觸發器本身就是一個事務,所以在觸發器裡面可以對修改數據進行一些特殊的檢查。如果不滿足可以利用事務回滾,撤銷操作。

Ø 創建觸發器

    語法

create trigger tgr_name
on table_name
with encrypion –加密觸發器
  for update...
as
  Transact-SQL
  # 創建insert類型觸發器
--創建insert插入類型觸發器
if (object_id('tgr_classes_insert', 'tr') is not null)
  drop trigger tgr_classes_insert
go
create trigger tgr_classes_insert
on classes
  for insert --插入觸發
as
  --定義變量
  declare @id int, @name varchar(20), @temp int;
  --在inserted表中查詢已經插入記錄信息
  select @id = id, @name = name from inserted;
  set @name = @name + convert(varchar, @id);
  set @temp = @id / 2;  
  insert into student values(@name, 18 + @id, @temp, @id);
  print '添加學生成功!';
go
--插入數據
insert into classes values('5班', getDate());
--查詢數據
select * from classes;
select * from student order by id;
   insert觸發器,會在inserted表中添加一條剛插入的記錄。
  # 創建delete類型觸發器
--delete刪除類型觸發器
if (object_id('tgr_classes_delete', 'TR') is not null)
  drop trigger tgr_classes_delete
go
create trigger tgr_classes_delete
on classes
  for delete --刪除觸發
as
  print '備份數據中……';  
  if (object_id('classesBackup', 'U') is not null)
    --存在classesBackup,直接插入數據
    insert into classesBackup select name, createDate from deleted;
  else
    --不存在classesBackup創建再插入
    select * into classesBackup from deleted;
  print '備份數據成功!';
go
--
--不顯示影響行數
--set nocount on;
delete classes where name = '5班';
--查詢數據
select * from classes;
select * from classesBackup;
  delete觸發器會在刪除數據的時候,將剛才刪除的數據保存在deleted表中。
  # 創建update類型觸發器
--update更新類型觸發器
if (object_id('tgr_classes_update', 'TR') is not null)
  drop trigger tgr_classes_update
go
create trigger tgr_classes_update
on classes
  for update
as
  declare @oldName varchar(20), @newName varchar(20);
  --更新前的數據
  select @oldName = name from deleted;
  if (exists (select * from student where name like '%'+ @oldName + '%'))
    begin
      --更新後的數據
      select @newName = name from inserted;
      update student set name = replace(name, @oldName, @newName) where name like '%'+ @oldName + '%';
      print '級聯修改數據成功!';
    end
  else
    print '無需修改student表!';
go
--查詢數據
select * from student order by id;
select * from classes;
update classes set name = '五班' where name = '5班';
   update觸發器會在更新數據後,將更新前的數據保存在deleted表中,更新後的數據保存在inserted表中。
  # update更新列級觸發器
if (object_id('tgr_classes_update_column', 'TR') is not null)
  drop trigger tgr_classes_update_column
go
create trigger tgr_classes_update_column
on classes
  for update
as
  --列級觸發器:是否更新了班級創建時間
  if (update(createDate))
  begin
    raisError('系統提示:班級創建時間不能修改!', 16, 11);
    rollback tran;
  end
go
--測試
select * from student order by id;
select * from classes;
update classes set createDate = getDate() where id = 3;
update classes set name = '四班' where id = 7;
   更新列級觸發器可以用update是否判斷更新列記錄;
  # instead of類型觸發器
    instead of觸發器表示並不執行其定義的操作(insert、update、delete)而僅是執行觸發器本身的內容。
    創建語法
create trigger tgr_name
on table_name
with encryption
  instead of update...
as
  T-SQL
   # 創建instead of觸發器
if (object_id('tgr_classes_inteadOf', 'TR') is not null)
  drop trigger tgr_classes_inteadOf
go
create trigger tgr_classes_inteadOf
on classes
  instead of delete/*, update, insert*/
as
  declare @id int, @name varchar(20);
  --查詢被刪除的信息,病賦值
  select @id = id, @name = name from deleted;
  print 'id: ' + convert(varchar, @id) + ', name: ' + @name;
  --先刪除student的信息
  delete student where cid = @id;
  --再刪除classes的信息
  delete classes where id = @id;
  print '刪除[ id: ' + convert(varchar, @id) + ', name: ' + @name + ' ] 的信息成功!';
go
--test
select * from student order by id;
select * from classes;
delete classes where id = 7;
   # 顯示自定義消息raiserror
if (object_id('tgr_message', 'TR') is not null)
  drop trigger tgr_message
go
create trigger tgr_message
on student
  after insert, update
as raisError('tgr_message觸發器被觸發', 16, 10);
go
--test
insert into student values('lily', 22, 1, 7);
update student set sex = 0 where name = 'lucy';
select * from student order by id;
  # 修改觸發器
alter trigger tgr_message
on student
after delete
as raisError('tgr_message觸發器被觸發', 16, 10);
go
--test
delete from student where name = 'lucy';
  # 啟用、禁用觸發器
--禁用觸發器
disable trigger tgr_message on student;
--啟用觸發器
enable trigger tgr_message on student;
  # 查詢創建的觸發器信息
--查詢已存在的觸發器
select * from sys.triggers;
select * from sys.objects where type = 'TR';
--查看觸發器觸發事件
select te.* from sys.trigger_events te join sys.triggers t
on t.object_id = te.object_id
where t.parent_class = 0 and t.name = 'tgr_valid_data';
--查看創建觸發器語句
exec sp_helptext 'tgr_message';
  # 示例,驗證插入數據
if ((object_id('tgr_valid_data', 'TR') is not null))
  drop trigger tgr_valid_data
go
create trigger tgr_valid_data
on student
after insert
as
  declare @age int,
      @name varchar(20);
  select @name = s.name, @age = s.age from inserted s;
  if (@age < 18)
  begin
    raisError('插入新數據的age有問題', 16, 1);
    rollback tran;
  end
go
--test
insert into student values('forest', 2, 0, 7);
insert into student values('forest', 22, 0, 7);
select * from student order by id;
  # 示例,操作日志
if (object_id('log', 'U') is not null)
  drop table log
go
create table log(
  id int identity(1, 1) primary key,
  action varchar(20),
  createDate datetime default getDate()
)
go
if (exists (select * from sys.objects where name = 'tgr_student_log'))
  drop trigger tgr_student_log
go
create trigger tgr_student_log
on student
after insert, update, delete
as
  if ((exists (select 1 from inserted)) and (exists (select 1 from deleted)))
  begin
    insert into log(action) values('updated');
  end
  else if (exists (select 1 from inserted) and not exists (select 1 from deleted))
  begin
    insert into log(action) values('inserted');
  end
  else if (not exists (select 1 from inserted) and exists (select 1 from deleted))
  begin
    insert into log(action) values('deleted');
  end
go
--test
insert into student values('king', 22, 1, 7);
update student set sex = 0 where name = 'king';
delete student where name = 'king';
select * from log;
select * from student order by id;

以上是本文給大家深入淺析sqlserver觸發器的全部內容,希望大家喜歡。

  1. 上一頁:
  2. 下一頁:
Copyright © 程式師世界 All Rights Reserved