在Group By查询中划分值

Question

如何构建这样的请求（Sql Server 2008 R2）：
（我需要每个结果的“平均价格”）

SELECT 
    CategoryId
  , SUM(Price) AS TotalPrice
  , SUM(Quantity) AS TotalQuantity
  -->, TotalPrice/TotalQuantity AS AveragePrice
FROM Products 
GROUP BY CategoryId

（如果可能的话，不再重新计算两个SUM ...）

Answer 1

没有重新计算......

SELECT *, A.TotalPrice / A.TotalQuantity AS AveragePrice
FROM (SELECT 
       CategoryId
       , SUM(Price) AS TotalPrice
       , SUM(Quantity) AS TotalQuantity
      FROM Products 
      GROUP BY CategoryId) AS A

Answer 2

SELECT  CategoryId, 
        SUM(Price) AS TotalPrice, 
        SUM(Quantity) AS TotalQuantity, 
        (SUM(Price) * 1.0 / SUM(Quantity) * 1.0) AS AveragePrice
FROM    Products 
GROUP   BY CategoryId

或者你可以使用CTE

WITH cte
AS
(
    SELECT  CategoryId, 
            SUM(Price) AS TotalPrice, 
            SUM(Quantity) AS TotalQuantity
    FROM    Products 
    GROUP   BY CategoryId
)
SELECT CategoryId,
       TotalPrice,
       TotalQuantity,
       TotalPrice / TotalQuantity * 1.0 AveragePrice
FROM   cte