欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

SQL Server的触发器详解

程序员文章站 2022-06-09 22:50:56
目录什么是触发器dml触发器分为:创建触发器创建insert类型触发器创建delete类型触发器创建update类型触发器update更新列级触发器instead of类型触发器创建instead o...

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。

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

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。

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

--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

--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;

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(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

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;

总结

本篇文章就到这里了,希望能够给你带来帮助,也希望您能够多多关注的更多内容!