SQL中MERGE关于更新、插入的一种用法

DECLARE @SJD_Code AS VARCHAR(24)
DECLARE @SJD_Nendo AS VARCHAR(4)

MERGE INTO D_SJD
USING (SELECT @SJD_Code  [SJD_Code],
              @SJD_Nendo [SJD_Nendo]) insertData
ON D_SJD.[SJD_Code] = insertData.SJD_Code
WHEN MATCHED THEN
  UPDATE SET [SJD_Nendo] = insertData.[SJD_Nendo]
WHEN NOT MATCHED THEN
  INSERT ( [SJD_Code],
           [SJD_Nendo] )
  VALUES ( insertData.[SJD_Code],
           insertData.[SJD_Nendo] );