SQL Server 2008的实用小道具——merger(转：http://database.ctocio.com.cn/18/11525518.shtml)

根据在另一个表中找到的差异在一个表中插入、更新或删除行，可以对两个表进行同步。

　　A. 使用 MERGE 在单个语句中对表执行 UPDATE 和 DELETE 操作

　　下面的示例使用 MERGE 根据 SalesOrderDetail 表中已处理的订单，每天更新 AdventureWorks 示例数据库中的 ProductInventory 表。通过减去每天对 SalesOrderDetail 表中的每种产品所下的订单数，更新 ProductInventory 表的 Quantity 列。如果某种产品的订单数导致该产品的库存量下降到 0 或更少，则会从 ProductInventory 表中删除该产品对应的行。

　　B. 借助派生的源表，使用 MERGE 对目标表执行 UPDATE 和 INSERT 操作

　　下面的示例使用 MERGE 以更新或插入行的方式来修改 SalesReason 表。当源表中的 NewName 值与目标表 (SalesReason) 的 Name 列中的值匹配时，就会更新此目标表中的 ReasonType 列。当 NewName 的值不匹配时，就会将源行插入到目标表中。此源表是一个派生表，它使用 Transact-SQL 行构造函数功能指定源表的多个行。有关在派生表中使用行构造函数的详细信息，请参阅 FROM (Transact-SQL)。

　　C. 将 MERGE 语句的执行结果插入到另一个表中

　　下例捕获从 MERGE 语句的 OUTPUT 子句返回的数据，并将该数据插入另一个表。MERGE 语句根据在 SalesOrderDetail 表中处理的订单，更新 ProductInventory 表的 Quantity 列。本示例捕获已更新的行，并将这些行插入用于跟踪库存变化的另一个表中

USE AdventureWorks; 
GO 
IF OBJECT_ID (N'Production.usp_UpdateInventory', N'P') 
IS NOT NULL DROP PROCEDURE Production.usp_UpdateInventory; 
GO 
CREATE PROCEDURE Production.usp_UpdateInventory 
@OrderDate datetime 
AS
MERGE Production.ProductInventory AS target 
USING (SELECT ProductID, SUM(OrderQty) FROM Sales.SalesOrderDetail AS sod 
JOIN Sales.SalesOrderHeader AS soh 
ON sod.SalesOrderID = soh.SalesOrderID 
AND soh.OrderDate = @OrderDate 
GROUP BY ProductID) AS source (ProductID, OrderQty) 
ON (target.ProductID = source.ProductID) 
WHEN MATCHED AND target.Quantity - source.OrderQty <= 0 
THEN DELETE
WHEN MATCHED 
THEN UPDATE SET target.Quantity = target.Quantity - source.OrderQty, 
target.ModifiedDate = GETDATE() 
OUTPUT $action, Inserted.ProductID, Inserted.Quantity, Inserted.ModifiedDate, Deleted.ProductID, 
Deleted.Quantity, Deleted.ModifiedDate; 
GO 
 
EXECUTE Production.usp_UpdateInventory '20030501'

USE AdventureWorks; 
GO 
MERGE INTO Sales.SalesReason AS Target 
USING (VALUES ('Recommendation','Other'), ('Review', 'Marketing'), ('Internet', 'Promotion')) 
AS Source (NewName, NewReasonType) 
ON Target.Name = Source.NewName 
WHEN MATCHED THEN
UPDATE SET ReasonType = Source.NewReasonType 
WHEN NOT MATCHED BY TARGET THEN
INSERT (Name, ReasonType) VALUES (NewName, NewReasonType) 
OUTPUT $action, inserted.*, deleted.*;

USE AdventureWorks; 
GO 
CREATE TABLE Production.UpdatedInventory 
(ProductID INT NOT NULL, LocationID int, NewQty int, PreviousQty int, 
CONSTRAINT PK_Inventory PRIMARY KEY CLUSTERED (ProductID, LocationID)); 
GO 
INSERT INTO Production.UpdatedInventory 
SELECT ProductID, LocationID, NewQty, PreviousQty 
FROM
( MERGE Production.ProductInventory AS pi 
USING (SELECT ProductID, SUM(OrderQty) 
FROM Sales.SalesOrderDetail AS sod 
JOIN Sales.SalesOrderHeader AS soh 
ON sod.SalesOrderID = soh.SalesOrderID 
AND soh.OrderDate BETWEEN '20030701' AND '20030731'
GROUP BY ProductID) AS src (ProductID, OrderQty) 
ON pi.ProductID = src.ProductID 
WHEN MATCHED AND pi.Quantity - src.OrderQty >= 0 
THEN UPDATE SET pi.Quantity = pi.Quantity - src.OrderQty 
WHEN MATCHED AND pi.Quantity - src.OrderQty <= 0 
THEN DELETE
OUTPUT $action, Inserted.ProductID, Inserted.LocationID, Inserted.Quantity AS NewQty, Deleted.Quantity AS PreviousQty) 
AS Changes (Action, ProductID, LocationID, NewQty, PreviousQty) WHERE Action = 'UPDATE'; 
GO