深入淺析SQL Server 觸發器

2024-08-31 01:03:16

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觸發器是一種特殊的存儲過程，觸發器是通過事件觸發可以自動調用執行的。在sql2005中，觸發器可以分為dml觸發器和ddl觸發器。下面通過本篇文章給大家深入淺析sqlserver觸發器，需要的朋友可以參考下

觸發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 什么是觸發器

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(之后觸發)

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之后觸發器才被觸發，且只能定義在表上。而instead of觸發器表示并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。當觸發器完成工作后，這兩張表就會被刪除。Inserted表的數據是插入或是修改后的數據，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，然后增加一條記錄。這樣在inserted和deleted表就都有update后的數據記錄了。注意的是：觸發器本身就是一個事務，所以在觸發器里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

--更新后的數據

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后，將更新前的數據保存在deleted表中，更新后的數據保存在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觸發器表示并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;