中位数计算不正确答案

【问题标题】：Median worked out incorrectly中位数计算不正确
【发布时间】：2015-03-20 08:20:55
【问题描述】：

我已经尝试了所有可能性来计算特定列的中值，但不断从 Excel 中获得不同的值。

我正在研究 SQL2008R2

这是我迄今为止尝试过的：

SELECT  Entity,
                BillPeriod,
                Cost,
                PatientDays,
                0 AS Median
        FROM GroupCTE
        UNION 
        SELECT  Entity,
                BillPeriod,
                Cost,
                PatientDays,
                0 AS Median
        FROM RegionCTE
                    UNION 
        SELECT  Entity,
                BillPeriod,
                Cost,
                PatientDays,
                0 AS Median
        FROM InstitutionCTE
        Union
        SELECT  'Median' as Entity,
                BillPeriod,
                0 as Cost,
                0 as PatientDays,
                (((
                    (SELECT MAX(Cost) FROM
                        (SELECT TOP 50 PERCENT Cost FROM InstitutionCTE WHERE Cost <> 0 ORDER BY Cost ASC) AS BottomHalf)
                    +
                    (SELECT MIN(Cost) FROM
                        (SELECT TOP 50 PERCENT Cost FROM InstitutionCTE WHERE Cost <> 0 ORDER BY Cost DESC) AS TopHalf)
                )) / 2)  AS Median

我在这里做错了什么吗？

我试过这个：Function to Calculate Median in Sql Server

谢谢

【问题讨论】：

你可以看这个，Itzik Ben-Gan 给出了一些如何计算中位数的好例子：youtube.com/watch?v=goyWzAu-AA0
此计算与中位数的定义不匹配。而 Excel 中位数函数可能正在实现中位数的确切公式。所以你会看到结果的不同。
(1) 提供一个计算不正确的例子。 (2) 如果cost是一个整数，那么你就是在做整数除法。
@GordonLinoff，与当前数据相比，与 SQL 结果相比，我得到了很大的不同：SQL - 401970.095 Excel - 397361.495。费用数据类型为浮点数。
计算大于和小于这些值的值的数量，并找出哪个是正确的。

标签： sql sql-server sql-server-2008-r2 median

【解决方案1】：

所以我设法解决了这个问题。问题是，由于某种原因，进行中位数计算得出的结果与 Excel 中位数函数的结果不同。

我创建了一个 TEMP 表并导入了我的 UNION 的结果，然后使用我的计算更新了 Median 列：

INSERT INTO #Temp
            SELECT  Entity,
                    BillPeriod,
                    ((Cost) / (PatientDays)) * 100 AS Cost,
                    PatientDays,
                    0 AS Median
            FROM GroupCTE
            UNION 
            SELECT  Entity,
                    BillPeriod,
                    ((Cost) / (PatientDays)) * 100 AS Cost,
                    PatientDays,
                    0 AS Median
            FROM RegionCTE
            UNION 
            SELECT  Entity,
                    BillPeriod,
                    ((Cost) / (PatientDays)) * 100 AS Cost,
                    PatientDays,
                    0 AS Median
            FROM InstitutionCTE
            UNION       
            SELECT  'Median' as Entity,
                    BillPeriod,
                    0 AS Cost,
                    0 AS PatientDays,
                    0 AS Median


            FROM InstitutionCTE
            GROUP BY Entity, BillPeriod, PatientDays

            UPDATE #Temp
            SET Median =    ((
                        ((SELECT MAX(Cost) FROM
                            (SELECT TOP 50 PERCENT Cost FROM #Temp WHERE Cost <> 0 ORDER BY Cost ASC) AS BottomHalf)
                        +
                        (SELECT MIN(Cost) FROM
                            (SELECT TOP 50 PERCENT Cost FROM #Temp WHERE Cost <> 0 ORDER BY Cost DESC) AS TopHalf)
                    )) / 2)     


SELECT * FROM #Temp
DROP TABLE #Temp

【讨论】：