触发器是一种特殊类型的存储过程，它不同于之前的我们介绍的存储过程。触发器主要是通过事件进行触发被自动调用执行的。而存储过程可以通过存储过程的名称被调用。

Ø 什么是触发器

    触发器对表进行插入、更新、删除的时候会自动执行的特殊存储过程。触发器一般用在check约束更加复杂的约束上面。触发器和普通的存储过程的区别是：触发器是当对某一个表进行操作。诸如：update、insert、delete这些操作的时候，系统会自动调用执行该表上对应的触发器。SQL Server 2005中触发器可以分为两类：DML触发器和DDL触发器，其中DDL触发器它们会影响多种数据定义语言语句而激发，这些语句有create、alter、drop语句。

    DML触发器分为：

    1、 after触发器（之后触发）

        a、 insert触发器

        b、 update触发器

        c、 delete触发器

    2、 instead of 触发器 （之前触发）

    其中after触发器要求只有执行某一操作insert、update、delete之后触发器才被触发，且只能定义在表上。而instead of触发器表示并不执行其定义的操作（insert、update、delete）而仅是执行触发器本身。既可以在表上定义instead of触发器，也可以在视图上定义。

    触发器有两个特殊的表：插入表（instered表）和删除表（deleted表）。这两张是逻辑表也是虚表。有系统在内存中创建者两张表，不会存储在数据库中。而且两张表的都是只读的，只能读取数据而不能修改数据。这两张表的结果总是与被改触发器应用的表的结构相同。当触发器完成工作后，这两张表就会被删除。Inserted表的数据是插入或是修改后的数据，而deleted表的数据是更新前的或是删除的数据。

    Update数据的时候就是先删除表记录，然后增加一条记录。这样在inserted和deleted表就都有update后的数据记录了。注意的是：触发器本身就是一个事务，所以在触发器里面可以对修改数据进行一些特殊的检查。如果不满足可以利用事务回滚，撤销操作。

Ø 创建触发器

    语法

create trigger tgr_name<br>on table_name<br>with encrypion –加密触发器<br>    for update...<br>as<br>    Transact-SQL

    # 创建insert类型触发器

--创建insert插入类型触发器<br>if (object_id(‘tgr_classes_insert‘, ‘tr‘) is not null)<br>    drop trigger tgr_classes_insert<br>go<br>create trigger tgr_classes_insert<br>on classes<br>    for insert --插入触发<br>as<br>    --定义变量<br>    declare @id int, @name varchar(20), @temp int;<br>    --在inserted表中查询已经插入记录信息<br>    select @id = id, @name = name from inserted;<br>    set @name = @name + convert(varchar, @id);<br>    set @temp = @id / 2;    <br>    insert into student values(@name, 18 + @id, @temp, @id);<br>    print ‘添加学生成功！‘;<br>go<br>--插入数据<br>insert into classes values(‘5班‘, getDate());<br>--查询数据<br>select * from classes;<br>select * from student order by id;

     insert触发器，会在inserted表中添加一条刚插入的记录。

    # 创建delete类型触发器

--delete删除类型触发器<br>if (object_id(‘tgr_classes_delete‘, ‘TR‘) is not null)<br>    drop trigger tgr_classes_delete<br>go<br>create trigger tgr_classes_delete<br>on classes<br>    for delete --删除触发<br>as<br>    print ‘备份数据中……‘;    <br>    if (object_id(‘classesBackup‘, ‘U‘) is not null)<br>        --存在classesBackup，直接插入数据<br>        insert into classesBackup select name, createDate from deleted;<br>    else<br>        --不存在classesBackup创建再插入<br>        select * into classesBackup from deleted;<br>    print ‘备份数据成功！‘;<br>go<br>--<br>--不显示影响行数<br>--set nocount on;<br>delete classes where name = ‘5班‘;<br>--查询数据<br>select * from classes;<br>select * from classesBackup;

   delete触发器会在删除数据的时候，将刚才删除的数据保存在deleted表中。

    # 创建update类型触发器

--update更新类型触发器<br>if (object_id(‘tgr_classes_update‘, ‘TR‘) is not null)<br>    drop trigger tgr_classes_update<br>go<br>create trigger tgr_classes_update<br>on classes<br>    for update<br>as<br>    declare @oldName varchar(20), @newName varchar(20);<br>    --更新前的数据<br>    select @oldName = name from deleted;<br>    if (exists (select * from student where name like ‘%‘+ @oldName + ‘%‘))<br>        begin<br>            --更新后的数据<br>            select @newName = name from inserted;<br>            update student set name = replace(name, @oldName, @newName) where name like ‘%‘+ @oldName + ‘%‘;<br>            print ‘级联修改数据成功！‘;<br>        end<br>    else<br>        print ‘无需修改student表！‘;<br>go<br>--查询数据<br>select * from student order by id;<br>select * from classes;<br>update classes set name = ‘五班‘ where name = ‘5班‘;

     update触发器会在更新数据后，将更新前的数据保存在deleted表中，更新后的数据保存在inserted表中。

    # update更新列级触发器

if (object_id(‘tgr_classes_update_column‘, ‘TR‘) is not null)<br>    drop trigger tgr_classes_update_column<br>go<br>create trigger tgr_classes_update_column<br>on classes<br>    for update<br>as<br>    --列级触发器：是否更新了班级创建时间<br>    if (update(createDate))<br>    begin<br>        raisError(‘系统提示：班级创建时间不能修改！‘, 16, 11);<br>        rollback tran;<br>    end<br>go<br>--测试<br>select * from student order by id;<br>select * from classes;<br>update classes set createDate = getDate() where id = 3;<br>update classes set name = ‘四班‘ where id = 7;

     更新列级触发器可以用update是否判断更新列记录；

    # instead of类型触发器

       instead of触发器表示并不执行其定义的操作（insert、update、delete）而仅是执行触发器本身的内容。

       创建语法

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

      # 创建instead of触发器

if (object_id(‘tgr_classes_inteadOf‘, ‘TR‘) is not null)<br>    drop trigger tgr_classes_inteadOf<br>go<br>create trigger tgr_classes_inteadOf<br>on classes<br>    instead of delete/*, update, insert*/<br>as<br>    declare @id int, @name varchar(20);<br>    --查询被删除的信息，病赋值<br>    select @id = id, @name = name from deleted;<br>    print ‘id: ‘ + convert(varchar, @id) + ‘, name: ‘ + @name;<br>    --先删除student的信息<br>    delete student where cid = @id;<br>    --再删除classes的信息<br>    delete classes where id = @id;<br>    print ‘删除[ id: ‘ + convert(varchar, @id) + ‘, name: ‘ + @name + ‘ ] 的信息成功！‘;<br>go<br>--test<br>select * from student order by id;<br>select * from classes;<br>delete classes where id = 7;

      # 显示自定义消息raiserror

if (object_id(‘tgr_message‘, ‘TR‘) is not null)<br>    drop trigger tgr_message<br>go<br>create trigger tgr_message<br>on student<br>    after insert, update<br>as raisError(‘tgr_message触发器被触发‘, 16, 10);<br>go<br>--test<br>insert into student values(‘lily‘, 22, 1, 7);<br>update student set sex = 0 where name = ‘lucy‘;<br>select * from student order by id;

    # 修改触发器

alter trigger tgr_message<br>on student<br>after delete<br>as raisError(‘tgr_message触发器被触发‘, 16, 10);<br>go<br>--test<br>delete from student where name = ‘lucy‘;

    # 启用、禁用触发器

--禁用触发器<br>disable trigger tgr_message on student;<br>--启用触发器<br>enable trigger tgr_message on student;

    # 查询创建的触发器信息

--查询已存在的触发器<br>select * from sys.triggers;<br>select * from sys.objects where type = ‘TR‘;<br><br>--查看触发器触发事件<br>select te.* from sys.trigger_events te join sys.triggers t<br>on t.object_id = te.object_id<br>where t.parent_class = 0 and t.name = ‘tgr_valid_data‘;<br><br>--查看创建触发器语句<br>exec sp_helptext ‘tgr_message‘;

    # 示例，验证插入数据

if ((object_id(‘tgr_valid_data‘, ‘TR‘) is not null))<br>    drop trigger tgr_valid_data<br>go<br>create trigger tgr_valid_data<br>on student<br>after insert<br>as<br>    declare @age int,<br>            @name varchar(20);<br>    select @name = s.name, @age = s.age from inserted s;<br>    if (@age < 18)<br>    begin<br>        raisError(‘插入新数据的age有问题‘, 16, 1);<br>        rollback tran;<br>    end<br>go<br>--test<br>insert into student values(‘forest‘, 2, 0, 7);<br>insert into student values(‘forest‘, 22, 0, 7);<br>select * from student order by id;

    # 示例，操作日志

if (object_id(‘log‘, ‘U‘) is not null)<br>    drop table log<br>go<br>create table log(<br>    id int identity(1, 1) primary key,<br>    action varchar(20),<br>    createDate datetime default getDate()<br>)<br>go<br>if (exists (select * from sys.objects where name = ‘tgr_student_log‘))<br>    drop trigger tgr_student_log<br>go<br>create trigger tgr_student_log<br>on student<br>after insert, update, delete<br>as<br>    if ((exists (select 1 from inserted)) and (exists (select 1 from deleted)))<br>    begin<br>        insert into log(action) values(‘updated‘);<br>    end<br>    else if (exists (select 1 from inserted) and not exists (select 1 from deleted))<br>    begin<br>        insert into log(action) values(‘inserted‘);<br>    end<br>    else if (not exists (select 1 from inserted) and exists (select 1 from deleted))<br>    begin<br>        insert into log(action) values(‘deleted‘);<br>    end<br>go<br>--test<br>insert into student values(‘king‘, 22, 1, 7);<br>update student set sex = 0 where name = ‘king‘;<br>delete student where name = ‘king‘;<br>select * from log;<br>select * from student order by id;

SQL Server 触发器

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