向 SQL 查询添加平均值

Question

我正在尝试创建一个查询来显示不同国家/地区之间的平均销售额，但我还想添加第 4 列，其中显示该国家/地区的总平均值...

这是我的查询，用于选择工作正常的国家/地区之间的平均值：

SELECT Avg([Sales]), [From Country],[To Country], 
FROM [DB]
GROUP by [From Country],[To Country]

但我还想添加第 4 列，显示 [From Country] 的总平均销售额，可以这样做吗？

Answer 1

在这里你必须小心。 您可以使用窗口函数，但要获得无偏平均值，您需要按总数计算总数：

SELECT [From Country], [To Country], Avg([Sales]), 
       SUM(SUM(Sales)) OVER (PARTITION BY [From Country]) / SUM(COUNT(*)) OVER (PARTITION BY [From Country])
FROM [DB]
GROUP by [From Country], [To Country];

请注意，结果不同于：

AVG(AVG(SALES)) OVER (PARTITION BY [From Country])

这是一个有偏见的（或加权的）平均值，它平等地对待每个TO COUNTRY 。

Answer 2

您还可以使用ROLLUP

SELECT [From Country], [To Country], [Avg], [Avg From]
FROM
(
    SELECT [From Country], [To Country]
    , AVG([Sales]) AS [Avg]
    , MAX(CASE WHEN GROUPING_ID([From Country], [To Country])  = 1 THEN AVG([Sales]) END) OVER (PARTITION BY [From Country]) AS [Avg From]
    , GROUPING_ID([From Country], [To Country]) AS GroupingId
    FROM [DB]
    GROUP BY [From Country], [To Country]
    WITH ROLLUP
) q
WHERE GroupingId = 0;

在这里测试