SQL 觸發器

觸發器是一種特殊類型的存儲過程,它不一樣於以前的咱們介紹的存儲過程。觸發器主要是經過事件進行觸發被自動調用執行的。而存儲過程能夠經過存儲過程的名稱被調用。html

Ø 什麼是觸發器web

    觸發器對錶進行插入、更新、刪除的時候會自動執行的特殊存儲過程。觸發器通常用在check約束更加複雜的約束上面。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做。諸如:update、insert、delete這些操做的時候,系統會自動調用執行該表上對應的觸發器。SQL Server 2005中觸發器能夠分爲兩類: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。數據庫

 

    DML觸發器分爲:app

    一、 after觸發器(以後觸發)ide

        a、 insert觸發器post

        b、 update觸發器測試

        c、 delete觸發器加密

 

    二、 instead of 觸發器 (以前觸發)url

 

    其中after觸發器要求只有執行某一操做insert、update、delete以後觸發器才被觸發,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做(insert、update、delete)而僅是執行觸發器自己。既能夠在表上定義instead of觸發器,也能夠在視圖上定義。spa

 

    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。有系統在內存中建立者兩張表,不會存儲在數據庫中。並且兩張表的都是隻讀的,只能讀取數據而不能修改數據。這兩張表的結果老是與被改觸發器應用的表的結構相同。當觸發器完成工做後,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。

 

 

對錶的操做

Inserted邏輯表

Deleted邏輯表

增長記錄(insert)

存放增長的記錄

刪除記錄(delete)

存放被刪除的記錄

修改記錄(update)

存放更新後的記錄

存放更新前的記錄

 

    Update數據的時候就是先刪除表記錄,而後增長一條記錄。這樣在inserted和deleted表就都有update後的數據記錄了。注意的是:觸發器自己就是一個事務,因此在觸發器裏面能夠對修改數據進行一些特殊的檢查。若是不知足能夠利用事務回滾,撤銷操做。

 

Ø 建立觸發器

    語法

create trigger tgr_name on table_name with encrypion –加密觸發器     for update... as     Transact-SQL

    # 建立insert類型觸發器

--建立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。

 

    # 建立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建立再插入         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,將剛纔刪除的數據保存在deleted表中。

 

    # 建立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:是否更新了班級建立時間     if (update(createDate))     begin         raisError('系統提示:班級建立時間不能修改!', 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;

     更新列級觸發器能夠用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做(insert、update、delete)而僅是執行觸發器自己的內容。

       建立語法

create trigger tgr_name on table_name with encryption     instead of update... as     T-SQL

   

      # 建立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';

    # 啓用、禁用觸發器

--禁用觸發器 disable trigger tgr_message on student; --啓用觸發器 enable trigger tgr_message on student;

    # 查詢建立的觸發器信息

--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';
--查看建立觸發器語句 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,操做日誌

 

 

 

 

 

 

 

 

 

 

 

 

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;
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