SQL Server 板机

? 什么是触发器

    触发器对表进行插入、更新、删除的时候会自己主动运行的特殊存储过程。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差别是：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，系统会自己主动调用运行该表上相应的触发器。SQL Server 2005中触发器能够分为两类：DML触发器和DDL触发器。当中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）

 

    当中after触发器要求仅仅有运行某一操作insert、update、delete之后触发器才被触发。且仅仅能定义在表上。而instead of触发器表示并不运行其定义的操作（insert、update、delete）而仅是运行触发器本身。既能够在表上定义instead of触发器，也能够在视图上定义。

 

    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。并且两张表的都是仅仅读的，仅仅能读取数据而不能改动数据。这两张表的结果总是与被改触发器应用的表的结构同样。当触发器完毕工作后，这两张表就会被删除。

Inserted表的数据是插入或是改动后的数据，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
添加记录（insert）	存放添加的记录	无
删除记录（delete）	无	存放被删除的记录
改动记录（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，然后添加一条记录。

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。所以在触发器里面能够对改动数据进行一些特殊的检查。假设不满足能够利用事务回滚，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 ‘加入学生成功。‘;
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表中加入一条刚插入的记录。

 

    # 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 ‘级联改动数据成功！‘;
        end
    else
        print ‘无需改动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：班级创建时间不能改动。‘, 16, 11);
        rollback tran;
    end
go
--測试
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;

     更新列级触发器能够用update是否推断更新列记录；

 

    # instead of类型触发器

       instead of触发器表示并不运行其定义的操作（insert、update、delete）而仅是运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;

   

      # 显示自己定义消息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;

    # 改动触发器

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‘;

    # 演示样例。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;

    # 演示样例，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;