如何获得关系代数中频率最高的元组？

Question

id | language
---------
01 | Java
---------
01 | Python
---------
01 | C#
---------
02 | Java

例如，01具有最高的频率，因为他学习最多的语言，那么我如何获得频率最高的id？

Answer 1

您可以加入CTE：

with x as (
select id, count(*) as c from my_table group by id
),
m as (select max(c) as t from x)
select x.id
  from x
  join m on x.c = m.t

Answer 2

select top 1 id, count(id) frequency 
from #mytable
group by id
order by frequency desc