SQL Merge 函数

第一次接触这个函数，贴出来供大家参考下。
ALTER TRIGGER [dbo].[DocumentStatisticsAdd] ON [dbo].[BatchDocument]
    FOR INSERT,UPDATE
AS
    BEGIN

    MERGE INTO DocumentStatistics AS dsTarget
    USING (SELECT I.[LastUser],I.[IsBackFromAARTO], BS.BaDoStName,
      DoTeName=CASE WHEN dt.DoTeTypeID='TMS_Section341' THEN 'S341'
           WHEN dt.DoTeTypeID='TMS_Section56' THEN 'S56'
           WHEN dt.DoTeTypeID='TMS_ProvincialSection56' THEN 'ProvincialS56'
           ELSE '' END
      FROM  Inserted I,dbo.BatchDocumentStatus BS,dbo.Batch B,dbo.DocumentTemplate DT
      WHERE I.BaDoStID=BS.BaDoStID AND I.BatchID=B.BatchID AND DT.DoTeID=B.DoTeID
      AND BS.BaDoStID=2 --BS.BaDoStName='Scanned'
      ) as dsSource
    ON   dsTarget.DoStUser = dsSource.LastUser
      AND dsTarget.DoStType=dsSource.DoTeName
      AND dsTarget.DoStDate=CONVERT(varchar(100), GETDATE(), 112)
      AND dsTarget.DoStHour = DATEPART(hh,GETDATE())          
    WHEN MATCHED    
    THEN
     UPDATE SET dsTarget.DoStScan = dsTarget.DoStScan + 1,dsTarget.DoStLastUpdateDate=GETDATE(),
        dsTarget.LastUser=dsTarget.LastUser
    WHEN NOT MATCHED
    THEN
     INSERT(DoStDate,DoStHour,DoStUser,DoStType,DoStScan,DoStEvidence ,DoStCapture,DoStValidate
         ,DoStQC,DoStExport,DoStFailed,DoStPark,DoStError,DoStCreateDate,DoStLastUpdateDate,LastUser)
     VALUES(CONVERT(varchar(100), GETDATE(), 112), DATEPART(hh,GETDATE()),
         dsSource.LastUser,dsSource.DoTeName,1,0,0,0,0,0,0,0,0,GETDATE(),GETDATE(),dsSource.LastUser);

    END