触发器在过去的10年中，即存储过程和ado.net称霸江湖期间是那么的重要，而现在，trigger显得不是那么必要的，我们很少将复杂的业务写在SQL里，当然也会没有机会写到trigger里了，可对于数据库本身来说，这东西还是要说说的，尤其是一些特殊场合，看看下面的触发器使用场合：
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这种结构很有意思，在SQLSERVER中实现两个数据库实时同步的方法有很多，比较简单的是“发布与订阅”，但说实话，这东西是有风显的，只要一个服务重新启动，它的同步数据就被删除了，即，后台数据库数据被删除，需要重新进行同步，感觉挺危险的，今天主要说的是一种传统的方法实现某些表数据的同步，即使用触发器实现数据的同步。
我们以Category表为例，前台数据库名为[background],后台数据库名为[background_copy]，当category表有数据插入时，[background_copy]表的数据自动实现插入，看一下代码部分吧：
USE [background]
GO
/****** Object: Trigger [dbo].[Trigger_Categoryinsert] Script Date: 09/10/2013 15:31:41 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[Trigger_Categoryinsert] ON [background].[dbo].[Category]
AFTER INSERT
AS
SET IDENTITY_INSERT background_copy.[dbo].[Category] ON
INSERT INTO background_copy.dbo.category
( [ID] ,
[ParentID] ,
[Level] ,
[Name] ,
[IsParent] ,
[CreateDate] ,
[Sortable]
)
SELECT [ID] ,
[ParentID] ,
[Level] ,
[Name] ,
[IsParent] ,
[CreateDate] ,
[Sortable]
FROM INSERTED
SET IDENTITY_INSERT background_copy.[dbo].[Category] OFF
我们可以看到，代码中使用SET IDENTITY_INSERT TableName ON/OFF命令，即，你的数据表主键是自增的，在同步时，需要去掉后台表的自增特性，这样才可以与前台的自增主键保持一致。
下面再看一下触发器的更新，使用场合介绍：当category表的name字段有更新后，自动同步到background_copy.[dbo].[Category] 表的name字段
USE [background]
GO
/****** Object: Trigger [dbo].[Trigger_CategoryUpdate] Script Date: 09/10/2013 16:06:31 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [dbo].[Trigger_CategoryUpdate] ON [dbo].[Category]
AFTER UPDATE
AS
IF UPDATE(Name)
BEGIN
UPDATE [background_copy].[dbo].[Category]
SET [Name] = ( SELECT name
FROM INSERTED
)
WHERE ID = ( SELECT id
FROM INSERTED
)
END
再来看一个更新表所有字段的，事实上就是把原来的记录删除，把新修改的记录插入就可以了，要求你注意的是自增主键的开关问题，看代码：
USE [BACKGROUND_COPY]
GO
/****** OBJECT: TRIGGER [DBO].[TRIGGER_CATEGORYUPDATE] SCRIPT DATE: 09/13/2013 18:01:00 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [DBO].[TRIGGER_CATEGORYUPDATE] ON [DBO].[CATEGORY]
AFTER UPDATE
AS
DELETE BACKGROUND_COPY2.DBO.CATEGORY
WHERE ID = ( SELECT ID
FROM INSERTED
) SET IDENTITY_INSERT BACKGROUND_COPY2.DBO.CATEGORY ON
INSERT INTO BACKGROUND_COPY2.DBO.CATEGORY
( ID ,
PARENTID ,
LEVEL ,
NAME ,
ISPARENT ,
CREATEDATE ,
SORTABLE
)
SELECT *
FROM INSERTED
SET IDENTITY_INSERT BACKGROUND_COPY2.DBO.CATEGORY OFF
看一下删除功能的触发器：
USE [BACKGROUND_COPY]
GO
/****** OBJECT: TRIGGER [DBO].[TRIGGER_CATEGORYDELETE] SCRIPT DATE: 09/13/2013 17:58:27 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER TRIGGER [DBO].[TRIGGER_CATEGORYDELETE] ON [DBO].[CATEGORY]
AFTER DELETE
AS
DELETE BACKGROUND_COPY2.DBO.CATEGORY
WHERE ID = ( SELECT ID
FROM DELETED
)
OK，现在我们的category表就可以实现自动同步了，呵呵。