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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。

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...as  Transact-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 classes  for 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 classes  for delete --删除触发as  print '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 classes  for updateas  declare @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！';    end  else    print '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 classes  for updateas  --列级触发器：是否更新了班级创建时间  if (update(createDate))  begin    raisError('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 encryption  instead of update...as  T-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 classes  instead of delete/*, update, insert*/as  declare @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 student  after 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 insertas  declare @age int,      @name varchar(20);  select @name = s.name, @age = s.age from inserted s;  if (@age < 18)  begin    raisError('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, deleteas  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');  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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