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這篇文章將為大家詳細講解有關(guān)如何深入淺析SQL Server 觸發(fā)器,文章內(nèi)容質(zhì)量較高,因此小編分享給大家做個參考,希望大家閱讀完這篇文章后對相關(guān)知識有一定的了解。
觸發(fā)器是一種特殊類型的存儲過程,它不同于之前的我們介紹的存儲過程。觸發(fā)器主要是通過事件進行觸發(fā)被自動調(diào)用執(zhí)行的。而存儲過程可以通過存儲過程的名稱被調(diào)用。
什么是觸發(fā)器
觸發(fā)器對表進行插入、更新、刪除的時候會自動執(zhí)行的特殊存儲過程。觸發(fā)器一般用在check約束更加復(fù)雜的約束上面。觸發(fā)器和普通的存儲過程的區(qū)別是:觸發(fā)器是當(dāng)對某一個表進行操作。諸如:update、insert、delete這些操作的時候,系統(tǒng)會自動調(diào)用執(zhí)行該表上對應(yīng)的觸發(fā)器。SQL Server 2005中觸發(fā)器可以分為兩類:DML觸發(fā)器和DDL觸發(fā)器,其中DDL觸發(fā)器它們會影響多種數(shù)據(jù)定義語言語句而激發(fā),這些語句有create、alter、drop語句。
DML觸發(fā)器分為:
1、 after觸發(fā)器(之后觸發(fā)) a、 insert觸發(fā)器 b、 update觸發(fā)器 c、 delete觸發(fā)器
2、 instead of 觸發(fā)器 (之前觸發(fā))
其中after觸發(fā)器要求只有執(zhí)行某一操作insert、update、delete之后觸發(fā)器才被觸發(fā),且只能定義在表上。而instead of觸發(fā)器表示并不執(zhí)行其定義的操作(insert、update、delete)而僅是執(zhí)行觸發(fā)器本身。既可以在表上定義instead of觸發(fā)器,也可以在視圖上定義。
觸發(fā)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(tǒng)在內(nèi)存中創(chuàng)建者兩張表,不會存儲在數(shù)據(jù)庫中。而且兩張表的都是只讀的,只能讀取數(shù)據(jù)而不能修改數(shù)據(jù)。這兩張表的結(jié)果總是與被改觸發(fā)器應(yīng)用的表的結(jié)構(gòu)相同。當(dāng)觸發(fā)器完成工作后,這兩張表就會被刪除。Inserted表的數(shù)據(jù)是插入或是修改后的數(shù)據(jù),而deleted表的數(shù)據(jù)是更新前的或是刪除的數(shù)據(jù)。
Update數(shù)據(jù)的時候就是先刪除表記錄,然后增加一條記錄。這樣在inserted和deleted表就都有update后的數(shù)據(jù)記錄了。注意的是:觸發(fā)器本身就是一個事務(wù),所以在觸發(fā)器里面可以對修改數(shù)據(jù)進行一些特殊的檢查。如果不滿足可以利用事務(wù)回滾,撤銷操作。
創(chuàng)建觸發(fā)器
語法
create trigger tgr_nameon table_namewith encrypion –加密觸發(fā)器 for update...as Transact-SQL # 創(chuàng)建insert類型觸發(fā)器--創(chuàng)建insert插入類型觸發(fā)器if (object_id('tgr_classes_insert', 'tr') is not null) drop trigger tgr_classes_insertgocreate trigger tgr_classes_inserton classes for insert --插入觸發(fā)as --定義變量 declare @id int, @name varchar(20), @temp int; --在inserted表中查詢已經(jīng)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(xué)生成功!';go--插入數(shù)據(jù)insert into classes values('5班', getDate());--查詢數(shù)據(jù)select * from classes;select * from student order by id; insert觸發(fā)器,會在inserted表中添加一條剛插入的記錄。 # 創(chuàng)建delete類型觸發(fā)器--delete刪除類型觸發(fā)器if (object_id('tgr_classes_delete', 'TR') is not null) drop trigger tgr_classes_deletegocreate trigger tgr_classes_deleteon classes for delete --刪除觸發(fā)as print '備份數(shù)據(jù)中……'; if (object_id('classesBackup', 'U') is not null) --存在classesBackup,直接插入數(shù)據(jù) insert into classesBackup select name, createDate from deleted; else --不存在classesBackup創(chuàng)建再插入 select * into classesBackup from deleted; print '備份數(shù)據(jù)成功!';go----不顯示影響行數(shù)--set nocount on;delete classes where name = '5班';--查詢數(shù)據(jù)select * from classes;select * from classesBackup; delete觸發(fā)器會在刪除數(shù)據(jù)的時候,將剛才刪除的數(shù)據(jù)保存在deleted表中。 # 創(chuàng)建update類型觸發(fā)器--update更新類型觸發(fā)器if (object_id('tgr_classes_update', 'TR') is not null) drop trigger tgr_classes_updategocreate trigger tgr_classes_updateon classes for updateas declare @oldName varchar(20), @newName varchar(20); --更新前的數(shù)據(jù) select @oldName = name from deleted; if (exists (select * from student where name like '%'+ @oldName + '%')) begin --更新后的數(shù)據(jù) select @newName = name from inserted; update student set name = replace(name, @oldName, @newName) where name like '%'+ @oldName + '%'; print '級聯(lián)修改數(shù)據(jù)成功!'; end else print '無需修改student表!';go--查詢數(shù)據(jù)select * from student order by id;select * from classes;update classes set name = '五班' where name = '5班'; update觸發(fā)器會在更新數(shù)據(jù)后,將更新前的數(shù)據(jù)保存在deleted表中,更新后的數(shù)據(jù)保存在inserted表中。 # update更新列級觸發(fā)器if (object_id('tgr_classes_update_column', 'TR') is not null) drop trigger tgr_classes_update_columngocreate trigger tgr_classes_update_columnon classes for updateas --列級觸發(fā)器:是否更新了班級創(chuàng)建時間 if (update(createDate)) begin raisError('系統(tǒng)提示:班級創(chuàng)建時間不能修改!', 16, 11); rollback tran; endgo--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(fā)器可以用update是否判斷更新列記錄; # instead of類型觸發(fā)器 instead of觸發(fā)器表示并不執(zhí)行其定義的操作(insert、update、delete)而僅是執(zhí)行觸發(fā)器本身的內(nèi)容。 創(chuàng)建語法create trigger tgr_nameon table_namewith encryption instead of update...as T-SQL # 創(chuàng)建instead of觸發(fā)器if (object_id('tgr_classes_inteadOf', 'TR') is not null) drop trigger tgr_classes_inteadOfgocreate trigger tgr_classes_inteadOfon 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--testselect * from student order by id;select * from classes;delete classes where id = 7; # 顯示自定義消息raiserrorif (object_id('tgr_message', 'TR') is not null) drop trigger tgr_messagegocreate trigger tgr_messageon student after insert, updateas raisError('tgr_message觸發(fā)器被觸發(fā)', 16, 10);go--testinsert 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(fā)器alter trigger tgr_messageon studentafter deleteas raisError('tgr_message觸發(fā)器被觸發(fā)', 16, 10);go--testdelete from student where name = 'lucy'; # 啟用、禁用觸發(fā)器--禁用觸發(fā)器disable trigger tgr_message on student;--啟用觸發(fā)器enable trigger tgr_message on student; # 查詢創(chuàng)建的觸發(fā)器信息--查詢已存在的觸發(fā)器select * from sys.triggers;select * from sys.objects where type = 'TR';--查看觸發(fā)器觸發(fā)事件select te.* from sys.trigger_events te join sys.triggers ton t.object_id = te.object_idwhere t.parent_class = 0 and t.name = 'tgr_valid_data';--查看創(chuàng)建觸發(fā)器語句exec sp_helptext 'tgr_message'; # 示例,驗證插入數(shù)據(jù)if ((object_id('tgr_valid_data', 'TR') is not null)) drop trigger tgr_valid_datagocreate trigger tgr_valid_dataon studentafter insertas 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(shù)據(jù)的age有問題', 16, 1); rollback tran; endgo--testinsert 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 loggocreate table log( id int identity(1, 1) primary key, action varchar(20), createDate datetime default getDate())goif (exists (select * from sys.objects where name = 'tgr_student_log')) drop trigger tgr_student_loggocreate trigger tgr_student_logon studentafter insert, update, deleteas 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'); endgo--testinsert 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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