在 Group By 查询中划分值

【问题标题】：divide values in a Group By query在 Group By 查询中划分值
【发布时间】：2013-12-06 10:31:49
【问题描述】：

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，无需重新计算两个 SUM 的一倍...）

【问题讨论】：

标签： sql sql-server sql-server-2008 group-by

【解决方案1】：

无需重新计算...

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

【讨论】：

【解决方案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

【讨论】：

试试看执行计划。