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
代码如下:
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 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'
代码如下:
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.*;
代码如下:
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.*;
代码如下:
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 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
