SQL Server 觸發器(內容非常不錯,轉載記錄)
觸發器是一種特殊型別的儲存過程,它不同於之前的我們介紹的儲存過程。觸發器主要是通過事件進行觸發被自動呼叫執行的。而儲存過程可以通過儲存過程的名稱被呼叫。
Ø 什麼是觸發器
觸發器對錶進行插入、更新、刪除的時候會自動執行的特殊儲存過程。觸發器一般用在check約束更加複雜的約束上面。觸發器和普通的儲存過程的區別是: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,系統會自動呼叫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資料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,也可以在檢視上定義。
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。有系統在記憶體中建立者兩張表,不會儲存在資料庫中。而且兩張表的都是隻讀的,只能讀取資料而不能修改資料。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表的資料是插入或是修改後的資料,而deleted表的資料是更新前的或是刪除的資料。
對錶的操作 |
Inserted邏輯表 |
Deleted邏輯表 |
增加記錄(insert) |
存放增加的記錄 |
無 |
刪除記錄(delete) |
無 |
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資料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後的資料記錄了。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資料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 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型別觸發器
--建立insert插入型別觸發器 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 --定義變數 declare @id int, @name varchar(20), @temp int; --在inserted表中查詢已經插入記錄資訊 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 '新增學生成功!'; go --插入資料 insert into classes values('5班', getDate()); --查詢資料 select * from classes; select * from student order by id;
insert觸發器,會在inserted表中新增一條剛插入的記錄。
# 建立delete型別觸發器
--delete刪除型別觸發器 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 '備份資料中……'; if (object_id('classesBackup', 'U') is not null) --存在classesBackup,直接插入資料 insert into classesBackup select name, createDate from deleted; else --不存在classesBackup建立再插入 select * into classesBackup from deleted; print '備份資料成功!'; go -- --不顯示影響行數 --set nocount on; delete classes where name = '5班'; --查詢資料 select * from classes; select * from classesBackup;
delete觸發器會在刪除資料的時候,將剛才刪除的資料儲存在deleted表中。
# 建立update型別觸發器
--update更新型別觸發器 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); --更新前的資料 select @oldName = name from deleted; if (exists (select * from student where name like '%'+ @oldName + '%')) begin --更新後的資料 select @newName = name from inserted; update student set name = replace(name, @oldName, @newName) where name like '%'+ @oldName + '%'; print '級聯修改資料成功!'; end else print '無需修改student表!'; go --查詢資料 select * from student order by id; select * from classes; update classes set name = '五班' where name = '5班';
update觸發器會在更新資料後,將更新前的資料儲存在deleted表中,更新後的資料儲存在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;
更新列級觸發器可以用update是否判斷更新列記錄;
# instead of型別觸發器
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。
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); --查詢被刪除的資訊,病賦值 select @id = id, @name = name from deleted; print 'id: ' + convert(varchar, @id) + ', name: ' + @name; --先刪除student的資訊 delete student where cid = @id; --再刪除classes的資訊 delete classes where id = @id; print '刪除[ id: ' + convert(varchar, @id) + ', name: ' + @name + ' ] 的資訊成功!'; go --test select * from student order by id; select * from classes; delete classes where id = 7;
# 顯示自定義訊息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;
# 查詢建立的觸發器資訊
--查詢已存在的觸發器 select * from sys.triggers; select * from sys.objects where type = 'TR'; --檢視觸發器觸發事件 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'; --檢視建立觸發器語句 exec sp_helptext 'tgr_message';
# 示例,驗證插入資料
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('插入新資料的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;
版權所有,轉載請註明出處 本文出自: http://www.cnblogs.com/hoojo/archive/2011/07/20/2111316.html