Home Database Mysql Tutorial 数据库综合系列之触发器

数据库综合系列之触发器

Jun 07, 2016 pm 03:22 PM
storage database series trigger process

触发器是一个特殊存储过程,它在插入,删除或修改特定表中的数据时触发执行,它比数据库本身标准的功能有更精细和更复杂的数据控制能力。 触发器与存储过程的唯一区别是触发器不能执行EXECUTE语句调用,而是在用户执行Transact-SQL语句时自动触发执行。 SQL

触发器是一个特殊存储过程,它在插入,删除或修改特定表中的数据时触发执行,它比数据库本身标准的功能有更精细和更复杂的数据控制能力。

触发器与存储过程的唯一区别是触发器不能执行EXECUTE语句调用,而是在用户执行Transact-SQL语句时自动触发执行。 

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。

作用:

a.允许/限制对表的修改

b.自动派生列,如自增字段

c.强制数据的一致性

d.提供审计和日志记录

e.防止无效的事务处理

f.启动复杂的业务逻辑

几个具体示例: instead of和after类似

1 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 manage
    for insert --插入触发
as
    --定义变量
    declare  @name varchar(20), @temp varchar(20);
    --在inserted表中查询已经插入记录信息
    select  @name = m_name,@temp=m_password from inserted;
    set @name = @name + 'buyingfei';
    insert into t_director values(@name, @temp,'男','2010-10-10','11111111112',1);
    print '添加成功!';
Copy after login

执行:
insert into manage values('经理','11111111112','男','2010-10-10','11111111112',2)
Copy after login

2 创建delete触发器

CREATE TRIGGER t1 ON  manage
for delete
AS 
If  (select count(*) from t_cash_housewoker  where m_id=t_cash_housewoker.m_id)>0
    BEGIN      
      Rollback tran
      Print 'the manager is userful, you can not delete it'     
   END	
Copy after login

触发语句:
delete from manage where m_id='3'
Copy after login

3 创建update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 manage
    for update
as
    --列级触发器:是否更新了班级创建时间
    if (update(m_name))
    begin
        raisError('系统提示:班级创建时间不能修改!', 16, 11);
        rollback tran;
    end
Copy after login

触发语句:
update manage set m_name='buyingfei' where m_id='1'
Copy after login
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