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
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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
--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_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;
# 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;
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