数据库技术:SQL Server 触发器详情

目录2、dml触发器分为1、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

目录
  • 2、 dml触发器分为

1、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:updateinsertdelete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createalterdrop语句。

2、 dml触发器分为

2.1 after触发器(之后触发)

a、 insert触发器

b、 update触发器

c、 delete触发器

2.2 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(insertupdatedelete)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

删除记录(delete)

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inserteddeleted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。

3、 创建触发器

语法

  create trigger tgr_name  on table_name  with encrypion –加密触发器      for update...  as      transact-sql    

3.1 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_insert  go  create trigger tgr_classes_insert  on 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。

 3.2  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_delete  go  create trigger tgr_classes_delete  on 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。

 3.3  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_update  go  create trigger tgr_classes_update  on classes      for update  as      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。

 3.4 update更新列级触发器

  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;      end  go  --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;

4、instead of类型触发器

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

创建语法:

  create trigger tgr_name  on table_name  with encryption      instead of update...  as      t-sql      

4.1 创建instead of触发器

  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  --test  select * from student order by id;  select * from classes;  delete classes where id = 7;           

4.2  显示自定义消息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触发器被触发', 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  修改触发器

  alter trigger tgr_message  on student  after delete  as raiserror('tgr_message触发器被触发', 16, 10);  go  --test  delete from student where name = 'lucy';    

4.4 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;    

4.5 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 t  on t.object_id = te.object_id  where t.parent_class = 0 and t.name = 'tgr_valid_data';    --查看创建触发器语句  exec sp_helptext 'tgr_message';  

4.6 示例,验证插入数据

  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('插入新数据的age有问题', 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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