SQL Server 觸發器詳情

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1、什麼是觸發器

    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。

2、 DML觸發器分為

2.1 after觸發器（之後觸發）

a、 insert觸發器

b、 update觸發器

c、 delete觸發器

2.2 instead of 觸發器 （之前觸發）

其中after觸發器要求隻有執行某一操作insert、update、delete之後觸發器才被觸發，且隻能定義在表上。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。而且兩張表的都是隻讀的，隻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，然後增加一條記錄。這樣在inserted和deleted表就都有update後的數據記錄瞭。註意的是：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。

3、 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

3.1 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。

 3.2  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。

 3.3  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。

 3.4 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：是否更新瞭班級創建時間
    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；

4、instead of類型觸發器

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。

創建語法：

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

4.1 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;

4.2  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;

4.3  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';

4.4 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;

4.5 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';

4.6 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;

4.7 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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