使用MERGE在单个语句中对表执行INSERT和UPDATE操作

一种常见的应用场景是在存在匹配行时更新表中的一个或多个列，或在不存在匹配行时将数据作为新行插入。 此操作一般通过将参数传递给包含相应 UPDATE 和 INSERT 语句的存储过程来执行。 借助 MERGE 语句，将可以在单个语句中一起执行这两项任务。 下面的示例

USE AdventureWorks2012;
GO
CREATE PROCEDURE dbo.InsertUnitMeasure
 @UnitMeasureCode nchar(3),
 @Name nvarchar(25)
AS 
BEGIN
 SET NOCOUNT ON;
-- Update the row if it exists. 
 UPDATE Production.UnitMeasure
	SET Name = @Name
	WHERE UnitMeasureCode = @UnitMeasureCode
-- Insert the row if the UPDATE statement failed.	
	IF (@@ROWCOUNT = 0 )
	BEGIN
	 INSERT INTO Production.UnitMeasure (UnitMeasureCode, Name)
	 VALUES (@UnitMeasureCode, @Name)
	END
END;
GO
-- Test the procedure and return the results.
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'Test Value';
SELECT UnitMeasureCode, Name FROM Production.UnitMeasure
WHERE UnitMeasureCode = 'ABC';
GO

-- Rewrite the procedure to perform the same operations using the MERGE statement.
-- Create a temporary table to hold the updated or inserted values from the OUTPUT clause.
CREATE TABLE #MyTempTable
 (ExistingCode nchar(3),
 ExistingName nvarchar(50),
 ExistingDate datetime,
 ActionTaken nvarchar(10),
 NewCode nchar(3),
 NewName nvarchar(50),
 NewDate datetime
 );
GO
ALTER PROCEDURE dbo.InsertUnitMeasure
 @UnitMeasureCode nchar(3),
 @Name nvarchar(25)
AS 
BEGIN
 SET NOCOUNT ON;

 MERGE Production.UnitMeasure AS target
 USING (SELECT @UnitMeasureCode, @Name) AS source (UnitMeasureCode, Name)
 ON (target.UnitMeasureCode = source.UnitMeasureCode)
 WHEN MATCHED THEN 
 UPDATE SET Name = source.Name
	WHEN NOT MATCHED THEN	
	 INSERT (UnitMeasureCode, Name)
	 VALUES (source.UnitMeasureCode, source.Name)
	 OUTPUT deleted.*, $action, inserted.* INTO #MyTempTable;
END;
GO
-- Test the procedure and return the results.
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'New Test Value';
EXEC InsertUnitMeasure @UnitMeasureCode = 'XYZ', @Name = 'Test Value';
EXEC InsertUnitMeasure @UnitMeasureCode = 'ABC', @Name = 'Another Test Value';

SELECT * FROM #MyTempTable;
-- Cleanup 
DELETE FROM Production.UnitMeasure WHERE UnitMeasureCode IN ('ABC','XYZ');
DROP TABLE #MyTempTable;
GO