SQL Server 触发器
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。
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_name On table_name With encrypion –加密触发器 For Update... As Transact -Sql
# 创建insert类型触发器
/************************************************************ * Code formatted by SoftTree SQL Assistant ?v6.0.70 * Time: 2014-10-15 10:42:34 ************************************************************/ --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。
# 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。
# 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?
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_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 =
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 On table_name With 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_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;
# 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;
# 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';
# 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 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';
# 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;
# 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;