分组 UNION ALL

您需要使用派生表或 CTE。使用派生表：

SELECT 
    A,
    SUM(B) AS SumQuantity,
    MIN(D) AS MinPrice             -- etc
FROM
  ( SELECT     CountryCode + ProductNumber + StockType AS A, 
               Quantity AS B, 
               Description AS C, 
               Price AS D

    FROM       dbo.vwSalesInvoiceWHandling
    UNION ALL
    SELECT     CountryCode + ProductNumber + StockType AS A,  
               Quantity AS B, 
               Description AS C, 
               Price AS D

    FROM       dbo.vwSalesInvoiceWOHandling
  ) 
    AS x      -- alias for the derived table
GROUP BY
    A ;

或者，在两个表中分组，然后全部联合。在这种情况下，您将需要派生表中的另一个分组依据，但它可能会更有效，主要是因为您可以更改按计算列的分组（CountryCode + ProductNumber + StockType)变为GROUP BY CountryCode, ProductNumber, StockType：

SELECT 
    CountryCode + ProductNumber + StockType AS A,
    SUM(B) AS SumQuantity,
    MIN(D) AS MinPrice             -- etc
FROM
  ( SELECT     CountryCode, ProductNumber, StockType, 
               SUM(Quantity) AS B, 
               MIN(Price) AS D

    FROM       dbo.vwSalesInvoiceWHandling
    GROUP BY   CountryCode, ProductNumber, StockType
    UNION ALL
    SELECT     CountryCode, ProductNumber, StockType,  
               SUM(Quantity) AS B, 
               MIN(Price) AS D

    FROM       dbo.vwSalesInvoiceWOHandling
    GROUP BY   CountryCode, ProductNumber, StockType
  ) 
    AS x      -- alias for the derived table
GROUP BY
    CountryCode, ProductNumber, StockType ;