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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。

对表的操作

Inserted逻辑表

Deleted逻辑表

增加记录（insert）

存放增加的记录

无

删除记录（delete）

无

存放被删除的记录

修改记录（update）

存放更新后的记录

存放更新前的记录

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_nameon table_namewith encrypion –加密触发器for update...asTransact-SQL # 创建insert类型触发器--创建insert插入类型触发器if (object_id('tgr_classes_insert', 'tr') is not null)drop trigger tgr_classes_insertgocreate trigger tgr_classes_inserton classesfor insert --插入触发as--定义变量declare @id int, @name varchar(20), @temp int;--在inserted表中查询已经插入记录信息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 '添加学生成功！';go--插入数据insert into classes values('5班', getDate());--查询数据select * from classes;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if (object_id('tgr_classes_delete', 'TR') is not null)drop trigger tgr_classes_deletegocreate trigger tgr_classes_deleteon classesfor delete --删除触发asprint '备份数据中……'; if (object_id('classesBackup', 'U') is not null)--存在classesBackup，直接插入数据insert into classesBackup select name, createDate from deleted;else--不存在classesBackup创建再插入select * into classesBackup from deleted;print '备份数据成功！';go----不显示影响行数--set nocount on;delete classes where name = '5班';--查询数据select * from classes;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if (object_id('tgr_classes_update', 'TR') is not null)drop trigger tgr_classes_updategocreate trigger tgr_classes_updateon classesfor updateasdeclare @oldName varchar(20), @newName varchar(20);--更新前的数据select @oldName = name from deleted;if (exists (select * from student where name like '%'+ @oldName + '%'))begin--更新后的数据select @newName = name from inserted;update student set name = replace(name, @oldName, @newName) where name like '%'+ @oldName + '%';print '级联修改数据成功！';endelseprint '无需修改student表！';go--查询数据select * from student order by id;select * from classes;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)drop trigger tgr_classes_update_columngocreate trigger tgr_classes_update_columnon classesfor updateas--列级触发器：是否更新了班级创建时间if (update(createDate))beginraisError('系统提示：班级创建时间不能修改！', 16, 11);rollback tran;endgo--测试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_nameon table_namewith encryptioninstead of update...asT-SQL # 创建instead of触发器if (object_id('tgr_classes_inteadOf', 'TR') is not null)drop trigger tgr_classes_inteadOfgocreate trigger tgr_classes_inteadOfon classesinstead of delete/*, update, insert*/asdeclare @id int, @name varchar(20);--查询被删除的信息，病赋值select @id = id, @name = name from deleted;print 'id: ' + convert(varchar, @id) + ', name: ' + @name;--先删除student的信息delete student where cid = @id;--再删除classes的信息delete classes where id = @id;print '删除[ id: ' + convert(varchar, @id) + ', name: ' + @name + ' ] 的信息成功！';go--testselect * from student order by id;select * from classes;delete classes where id = 7; # 显示自定义消息raiserrorif (object_id('tgr_message', 'TR') is not null)drop trigger tgr_messagegocreate trigger tgr_messageon studentafter insert, updateas raisError('tgr_message触发器被触发', 16, 10);go--testinsert into student values('lily', 22, 1, 7);update student set sex = 0 where name = 'lucy';select * from student order by id; # 修改触发器alter trigger tgr_messageon studentafter deleteas raisError('tgr_message触发器被触发', 16, 10);go--testdelete from student where name = 'lucy'; # 启用、禁用触发器--禁用触发器disable trigger tgr_message on student;--启用触发器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select * from sys.triggers;select * from sys.objects where type = 'TR';--查看触发器触发事件select te.* from sys.trigger_events te join sys.triggers ton t.object_id = te.object_idwhere t.parent_class = 0 and t.name = 'tgr_valid_data';--查看创建触发器语句exec sp_helptext 'tgr_message'; # 示例，验证插入数据if ((object_id('tgr_valid_data', 'TR') is not null))drop trigger tgr_valid_datagocreate trigger tgr_valid_dataon studentafter insertasdeclare @age int,@name varchar(20);select @name = s.name, @age = s.age from inserted s;if (@age < 18)beginraisError('插入新数据的age有问题', 16, 1);rollback tran;endgo--testinsert 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 loggocreate table log(id int identity(1, 1) primary key,action varchar(20),createDate datetime default getDate())goif (exists (select * from sys.objects where name = 'tgr_student_log'))drop trigger tgr_student_loggocreate trigger tgr_student_logon studentafter insert, update, deleteasif ((exists (select 1 from inserted)) and (exists (select 1 from deleted)))begininsert into log(action) values('updated');endelse if (exists (select 1 from inserted) and not exists (select 1 from deleted))begininsert into log(action) values('inserted');endelse if (not exists (select 1 from inserted) and exists (select 1 from deleted))begininsert into log(action) values('deleted');endgo--testinsert 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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