“无法绑定多部分标识符”错误

Question

I'm using SQL Server 2005. I get this error:

*The multi-part identifier "ms.MOP_desc" could not be bound.*

I tested each of the two select queries and they worked fine individually, but I got the error when I union those queries. Can I anyone tell me what went wrong with this query? Thank you.

SELECT SUM(Amount) AS TotalAmount, ms.MOP_desc
FROM 
(
    SELECT SUM(hd.delivery_value) AS Amount, ms.MOP_desc
    FROM TRANSACTION_HEADER AS th 
        INNER JOIN TRANSACTION_DETAIL AS td 
            ON th.transaction_number = td.transaction_number 
        LEFT JOIN hose_delivery hd 
            ON td.delivery_id = hd.delivery_id 
        LEFT JOIN product pr 
            ON pr.product_id = td.product_id
        INNER JOIN MOP_Setting AS ms 
            ON hd.MOP_ID = ms.MOP_ID  
    WHERE hd.delivery_value > 0 
        AND (th.USER_PERIOD_ID IN (13))
        AND (hd.MOP_ID  IN (1))
        AND hd.Cleared_By != '0'
    GROUP BY ms.MOP_desc

    UNION ALL

    SELECT  SUM(td.quantity * td.price_sold) AS Amount, ms.MOP_desc 
    FROM TRANSACTION_HEADER AS th 
        INNER JOIN TRANSACTION_DETAIL AS td 
            ON th.transaction_number = td.transaction_number 
        INNER JOIN MOP_Setting AS ms 
            ON th.MOP_ID = ms.MOP_ID  
    WHERE (th.USER_PERIOD_ID IN (13))
        AND (th.MOP_ID  IN (1))
    GROUP BY ms.MOP_desc
)t

Answer 1

Because the result from the UNION ed query is a rowset that you've given the alias t to - the ms alias is no longer applicable:

SELECT SUM(Amount) AS TotalAmount, t.MOP_desc
FROM 
(
...
)t

If this really is a second SUM step here, you'll need a outer GROUP BY clause also.

Answer 2

When you select from a subselect instead of a table, the column names from the subselect are not exposed to the outer select

Use

SELECT SUM(Amount) AS TotalAmount, mop
FROM 
(
  SELECT SUM(hd.delivery_value) AS Amount, ms.MOP_desc as mop
  FROM TRANSACTION_HEADER AS th 
      INNER JOIN TRANSACTION_DETAIL AS td 
...