SQL SERVER 觸發(fā)器介紹
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。
Ø 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)器應用的表的結(jié)構(gòu)相同。當觸發(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)。
對表的操作 |
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) |
存放更新后的記錄 |
存放更新前的記錄 |
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,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回滾,撤銷操作。
Ø 創(chuàng)建觸發(fā)器
語法
create trigger tgr_name on table_name with 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_insert go create trigger tgr_classes_insert on 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_delete go create trigger tgr_classes_delete on 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_update go create trigger tgr_classes_update on classes for update as 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_column go create trigger tgr_classes_update_column on classes for update as --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; 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(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_name on table_name with 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_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(fā)器被觸發(fā)', 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(fā)器 alter trigger tgr_message on student after delete as raisError('tgr_message觸發(fā)器被觸發(fā)', 16, 10); go --test delete 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 t on t.object_id = te.object_id where 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_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(shù)據(jù)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;
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