包括分组查询的中位数。

Question

我有这个查询需要绘制图表。
该图将显示每个位置的患者总数、患者最长等待时间（分钟）和患者等待时间中值。我需要在我的查询中包含中位数，这就是我遇到的问题。

示例原始数据：

到目前为止我有查询 w/o 中位数：

    SELECT 
[Location],
      count([Patient_Number]) Total,
      MAX([WaitTime_Min]) LongWait
     
  FROM MyTable
  where
  [Location] in ('AMB', 'PEDS', 'WALK')
  and [EDNurse] is NULL
  group by [Location]

输出：

我需要帮助获取每个位置的 WaitTime 的最后一列中位数（来自原始数据）。任何帮助，将不胜感激;谢谢！！

期望的输出：

Answer 1

在 Sqlserver 2012 中有 PERCENTILE_CONT(for continues values), PERCENTILE_DISC(for discrete value) 方法可以做到这一点。你可以阅读更多相关信息 here.

SELECT 
[Location],
      count([Patient_Number]) Total,
      MAX([WaitTime_Min]) LongWait,
     max(MedianDisc) MedianDisc, -- Discrete median
     max(MedianCont) MedianCont -- continues median
  FROM (
          select  m.*, PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY WaitTime_Min)   
                            OVER (PARTITION BY [Location]) AS MedianCont  
      ,PERCENTILE_DISC(0.5) WITHIN GROUP (ORDER BY WaitTime_Min)   
                            OVER (PARTITION BY [Location]) AS MedianDisc
            from myTable m
             where
  [Location] in ('AMB', 'PEDS', 'WALK')
  and [EDNurse] is NULL
   
  )tt
 
  group by [Location]

更新：基于 Aaron 评论的此方法中的性能问题，我为中位数添加了一个纯 SQL 计算：

select  [Location], 
        count([Patient_Number]) Total,
        MAX([WaitTime_Min]) LongWait,
        AVG(1.0 * LongWait) As Median
FROM
(
    SELECT [Location],
       [Patient_Number]  Total,
       [WaitTime_Min]  LongWait
        , ra=row_number() over (partition by [Location] order by [WaitTime_Min])
        , rd=row_number() over (partition by [Location] order by [WaitTime_Min] desc)
    from myTable m
    where [Location] in ('AMB', 'PEDS', 'WALK')
      and [EDNurse] is NULL
) as x
where ra between rd-1 and rd + 1
group by [Location]

包括分组查询的中位数。

Include Medians for grouped query .

sql

sql-server

sql-server-2012