SELECT     dbo.Categories.CategoryName, dbo.Products.ProductName, SUM(CONVERT(money, (dbo.[Order Details].UnitPrice * dbo.[Order Details].Quantity) 
                      * (1 - dbo.[Order Details].Discount) / 100) * 100) AS ProductSales
FROM         dbo.Categories INNER JOIN
                      dbo.Products ON dbo.Categories.CategoryID = dbo.Products.CategoryID INNER JOIN
                      dbo.Orders INNER JOIN
                      dbo.[Order Details] ON dbo.Orders.OrderID = dbo.[Order Details].OrderID ON dbo.Products.ProductID = dbo.[Order Details].ProductID
WHERE     (dbo.Orders.ShippedDate BETWEEN '19970101' AND '19971231')
GROUP BY dbo.Categories.CategoryName, dbo.Products.ProductName

SELECT dbo.Categories.CategoryName, dbo.Products.ProductName, SUM(                   --10
           CONVERT(
               MONEY, (dbo.[Order Details].UnitPrice*dbo.[Order Details].Quantity) 
              *(1- dbo.[Order Details].Discount)/100
           )*100
       ) AS ProductSales  
FROM dbo.Categories  --1
    INNER JOIN dbo.Products  --3
        ON  dbo.Categories.CategoryID = dbo.Products.CategoryID --2
    INNER JOIN dbo.Orders --7
    INNER JOIN dbo.[Order Details] --5
        ON  dbo.Orders.OrderID = dbo.[Order Details].OrderID --6
        ON  dbo.Products.ProductID = dbo.[Order Details].ProductID --4
WHERE (dbo.Orders.ShippedDate BETWEEN '19970101' AND '19971231') --8
GROUP BY dbo.Categories.CategoryName, dbo.Products.ProductName --9

------解决方案--------------------

SQL code
SQL Select语句完整的执行顺序： 

1、from子句组装来自不同数据源的数据； 
2、where子句基于指定的条件对记录行进行筛选； 
3、group by子句将数据划分为多个分组； 
4、使用聚集函数进行计算； 
5、使用having子句筛选分组； 
6、计算所有的表达式； 
7、使用order by对结果集进行排序。 


另外:一个查询语句各个部分的执行顺序: 
--8)  SELECT (9) DISTINCT (11) <TOP_specification> <select_list> 
--(1)  FROM <left_table> 
--(3)    <join_type> JOIN <right_table> 
--(2)      ON <join_condition> 
--(4)  WHERE <where_condition> 
--(5)  GROUP BY <group_by_list> 
--(6)  WITH {CUBE | ROLLUP} 
--(7)  HAVING <having_condition> 
--(10) ORDER BY <order_by_list>