问SQL MS Access的嵌套子查询

EN

SELECT [doc type]
     , [customer number]
     , COUNT([customer number]) As CountCustomerNumber
     , SUM(IIF([open_amount]>0, [open_amount], 0)) AS sum_open_amount_pos   
     , SUM(IIF([open_amount]<0, [open_amount], 0)) As sum_open_amount_neg         
FROM 
      (SELECT d.[customer number] & d.[membership number] AS CustMemb
            , d.[customer number]
            , agg.[doc type]
            , SUM(agg.[TotalSubOpenAmount]) AS SumOpenAmount
        FROM  (SELECT [doc type]
                    , [customer number]
                    , SUM([open amount]) AS TotalSubOpenAmount
               FROM   data
               WHERE  [doc type] = 'RU' 
               GROUP BY [doc type]
                      , [customer number]
              ) agg
        INNER JOIN [data] d                                   
           ON  d.[customer number] = agg.[customer number]
        GROUP  BY d.[customer number] & d.[membership number]
                , d.[customer number]
                , agg.[doc type]
      ) AS sub
GROUP  BY [doc type]
        , [customer number]
HAVING COUNT([customer number]) = 1

SELECT [doc type]
     , [customer number]
     , COUNT([customer number]) As CountCustomerNumber
     , SUM(IIF([open_amount]>0, [open_amount], 0)) AS sum_open_amount_pos   
     , SUM(IIF([open_amount]<0, [open_amount], 0)) As sum_open_amount_neg         
FROM 
      (
-- This is the part in which the field open_amount should be fetched.
) AS sub
GROUP  BY [doc type]
        , [customer number]
HAVING COUNT([customer number]) = 1