通过GroupBy获取模式值

Question

我有一些这样的数据

(AID,Answer)
(1,A)
(1,A)
(1,A)
(1,B)
(1,B)
(1,C)

(2,C)
(2,C)
(2,C)
(2,B)
(2,B)
(3,A)

我想按AID进行分组，并在每组中尽可能多地使用Answer。

结果：

(1,A)

(2,C)

使用SQL工具。

Answer 1

模式是最常见的值。最简单的方法是使用聚合和row_number()：

select aid, answer
from (select aid, answer, count(*) as cnt,
             row_number() over (partition by aid order by count(*) desc) as seqnum
      from t
      group by aid, answer
     ) aa
where seqnum = 1;