来看看老外的例子，例子有不正确的地方，

 http://www.kodyaz.com/t-sql/sql-merge-command-for-summary-table.aspx

Create Trigger trMergeProductSummary on ProductDetails
 After Insert, Update, Delete
AS
BEGIN

;Merge ProductSummary
Using (
 SELECT
  i.ProductId,
  i.ProductName,
  i.ProductNumber,
  i.CategoryId,
  i.ContactPerson,
  i.UpdateDate
 from inserted i
) MergeData ON ProductSummary.ProductId = MergeData.ProductId
 WHEN MATCHED THEN
 UPDATE SET
  ProductSummary.ProductName = MergeData.ProductName,
  ProductSummary.ProductNumber = MergeData.ProductNumber,
  ProductSummary.CategoryId = MergeData.CategoryId,
  ProductSummary.ContactPerson = MergeData.ContactPerson,
  ProductSummary.UpdateDate = GetDate()
 WHEN NOT MATCHED BY TARGET THEN
 INSERT VALUES (ProductId, ProductName, ProductNumber, CategoryId, ContactPerson, GetDate())
 WHEN NOT MATCHED BY SOURCE THEN DELETE;

END
GO

insert into ProductDetails (productname, productnumber, contactperson)
 values ('SQL Data Compare Tool', 'SQL-DC-001', 'Eralper Yilmaz')
 go 3
select * from ProductDetails
select * from ProductSummary

当运行下面语句时，ProductSummary 只有一条记录:而不是我们期望的三条
当运行下面语句时，ProductSummary 中的数据被消除：

注意，

当delete时trigger 中的inserted没有数据，所以会清空ProductSummary 表：

WHEN NOT MATCHED BY SOURCE THEN DELETE--source is empty, so it will clear all data in table ProductSummary 

下面是merge trigger 的实现

IF OBJECT_ID('[gomac].[T_INSERT_AvSysCodes]', 'TR') IS NOT NULL
BEGIN
    DROP TRIGGER [gomac].[T_INSERT_AvSysCodes]
END
GO 
CREATE TRIGGER [gomac].[T_INSERT_AvSysCodes]
ON [gomac].[AVSYSCODES]
FOR  INSERT, DELETE, UPDATE
AS
set nocount on
DECLARE @count        BIGINT = 0,
        @rowid        BIGINT = 1, 
        @sql          NVARCHAR(MAX) = N'',
        @sqlmerge     NVARCHAR(3000) = N'', 
		@action       NVARCHAR(20)='',
        @RECID        BIGINT  
if exists(select 1 from tempdb..sysobjects where id=object_id('tempdb..#tmp'))
	DROP TABLE #tmp
IF EXISTS(SELECT * FROM   INSERTED) AND NOT EXISTS(SELECT * FROM   DELETED) ----INSERT
BEGIN
		SET @action='INSERT'
END	
ELSE IF NOT EXISTS(SELECT * FROM   INSERTED)AND EXISTS(SELECT * FROM   DELETED) ----DELETE
BEGIN
	   SET @action='DELETE'
END
ELSE IF EXISTS(SELECT * FROM   INSERTED) AND EXISTS(SELECT * FROM   DELETED) -----UPDATE
BEGIN
	   SET @action='UPDATE'
END
SELECT row_number()OVER(ORDER BY dataareaid) rowid,DESCRIPTION,code,category,GETDATE() Modifieddatetime,
Modifiedby,GETDATE() Createddatetime,CreatedBy,dataareaid,1 Recversion,NULL Recid ,@ACTION AS [ACTION] INTO #tmp FROM 
(
	select * from inserted
	union 
	select * from deleted
) as a        
SELECT @count=@@rowcount
IF @action='INSERT' ----INSERT
BEGIN	
	WHILE @rowid<=@count
	BEGIN
		EXEC  DBO.UP_Get_Axapta_Seqno 'AvSysCodesAX',@RECID OUTPUT
		UPDATE #tmp SET recid=@recid WHERE rowid=@rowid
		SET @rowid+=1
	END	
END

;MERGE dbo.AvSysCodesAX d USING  #tmp s 
		ON d.dataareaid = s.dataareaid AND d.category = s.category AND  d.code = s.code		 
		WHEN NOT matched  THEN 
		INSERT ( DESCRIPTION,code,category,Modifieddatetime,Modifiedby,Createddatetime,CreatedBy,dataareaid, Recversion,Recid)VALUES 
         ( S.DESCRIPTION,S.code,S.category,S.Modifieddatetime,S.Modifiedby,S.Createddatetime,S.CreatedBy,S.dataareaid,S.Recversion,S.Recid) 
		WHEN matched AND S.ACTION='UPDATE' THEN    
		UPDATE	SET		  
			 d.[DESCRIPTION]    = s.[DESCRIPTION] , 
			 d.code				= s.code, 
			 d.category			= s.category, 
			 d.Modifieddatetime	= s.Modifieddatetime, 
			 d.Modifiedby	    = s.Modifiedby, 
			 d.dataareaid		= s.dataareaid 		
		WHEN  matched AND S.ACTION='DELETE' THEN 
		DELETE ;
if exists(select 1 from tempdb..sysobjects where id=object_id('tempdb..#tmp'))
DROP TABLE #tmp  
GO 

1. merge的源是第一次触发的inserted和deleted,这点不同于物理表，datasource 用inserted union deleted
2. 在WHEN  matched AND S.ACTION=‘DELETE‘ THEN delete;
3. 没有trigger row by row,seem currsor as the last choice.

存用

sql server 2012 merge的使用，同构表merger,异构表merge, 当merge 与trigger 同时使用时较容易出错