对于 旧 版本,可以使用相关子查询:
SELECT s.Product_ID, c.Category_Name,
(SELECT SUM(SS.Sales_Value) / SUM(SS.Sales_Quantity)
FROM Sales SS
WHERE SS.Category_ID = S.Category_ID
) AS average_sales_price
FROM Sales s JOIN
Categories c
ON c.Category_ID = s.Category_ID;
这是SQL Fiddle。