触发器

触发器

概念

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。

    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。

触发器语法

创建触发器

create trigger tgr_name

on table_name

with encrypion –加密触发器

    for update...

as

    Transact-SQL

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。

   

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。

   

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

   

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;