使用case和aggregate语句将值拆分为四分位数的sql server

Question

我有一个如下所示的Employee数据集。开始日期是员工的雇用日期，结束日期是员工离开雇主的日期。两者均为日期数据类型。

Gender   StartDate       EndDate
 M       2010-04-30      2013-06-18
 F       2010-01-09      2015-06-19
 M       2009-09-08      2014-08-13

我想根据平均工作月数将员工数据划分为四分位数。结果还包括雇员总数（“雇员”列），男性雇员的百分比，女性雇员的百分比以及平均受雇月数。请在下面找到预期的结果：

Quartile    Employee    %Male   %Female   AvgMonths
1             25        50.00    50.00     10
2             25        50.00    50.00     10

请在下面找到我的查询，我不知道在哪里可以将四分位数计算添加到查询中。

declare @current date;
set @current='2012-12-31';

select count(*) as Employees,
       cast(cast(AVG(CASE WHEN Gender = 'M' THEN 1.0 ELSE 0 END)*100 as decimal(18,2)) as nvarchar(5)) +'%' as Male,
       cast(cast(AVG(CASE WHEN Gender = 'F' THEN 1.0 ELSE 0 END)*100 as decimal(18,2)) as nvarchar(5)) +'%' as Female,
       AVG(CASE WHEN EndDate is null then DATEDIFF(MONTH, StartDate, @current)
                when EndDate is not null then DATEDIFF(MONTH, StartDate, EndDate)
           end) as AvgMonths
from dbo.DimEmployee

Answer 1

您可以使用rank()和count(*)作为窗口函数来计算四分位数：

select floor( rnk * 4.0 / cnt ) as quartile,
       count(*) as Employees,
       cast(cast(AVG(CASE WHEN Gender = 'M' THEN 1.0 ELSE 0 END)*100 as decimal(18,2)) as nvarchar(5)) + '%' as Male,
       cast(cast(AVG(CASE WHEN Gender = 'F' THEN 1.0 ELSE 0 END)*100 as decimal(18,2)) as nvarchar(5)) + '%' as Female,
       AVG(num_months * 1.0) as AvgMonths
from (select e.*,
             rank() over (partition by datediff(month, startdate, coalesce(enddate, @current))) - 1 as rnk,
             count(*) over () as cnt,
             datediff(month, startdate, coalesce(enddate, @current)) as num_months
      from dbo.DimEmployee e
     ) e
group by floor( rnk * 4.0 / cnt )