使用min（），count（），having子句的组合使用聚集的sql

Question

尝试查找允许我按组对名进行计数的代码，然后返回计数最少的名称。

样本数据：-

PersonGroup   FirstName
------------------------
A             Bob
A             Mary
A             Bob
A             Bob
B             Michelle
B             Michelle
B             Greg
B             Greg
B             Michelle
C             Cindy
C             Michelle
C             Michelle
D             Rod
D             Rod
D             Rod
D             Rod
D             Rod
D             Mary
D             Mary
D             Mary
D             Mary
D             Mary
D             Mary

需要的输出：

PersonGroup   FirstName    Count
--------------------------------
    A         Mary           1
    B         Greg           2
    C         Cindy          1
    D         Rod            5

“名字”列的名称在组中最少出现

“计数”列中的“名称”计数每组出现次数最少

到目前为止，这是我的代码，但是每个名称都将返回，

select
    PersonType,
    FirstName,
    count (firstName) as mycount
from
    [Person].[Person]
group by 
    FirstName,
    [PersonType]
having 
    count(firstName) = (select min(a.cnt)
                        from 
                             (select count(firstname) as cnt 
                              from [Person].[Person] 
                              group by [FirstName]) as a)
order by 
    PersonType desc

Answer 1

您可以使用row_number（）

select a.*
from (select PersonType,FirstName ,count (firstName) as mycount, 
             row_number() over (partition by PersonType order by count(*)) as rn
      from [Person].[Person]
     group by FirstName,[PersonType]
     ) a
where rn= 1; 

Answer 2

使用窗口功能8

row_number()

demo link