SQL query: Find the element with the highest frequency

Question

I'm trying to write a SQL query to find the mode, i.e. the element that occurs more often than other elements. For example:

2,2,1,1---->在这里，输出应该为空（1和2都出现了两次）

    3,3,3----->在这里，输出也应该为空（没有第二个元素）

    3,3,1----->在这里，输出应该是3。（3的出现次数大于1的出现次数）

Here are the 3 conditions used to find it. How can I implement it?

Answer 1

You can count the number of values ​​to find the most frequent value, and you can also filter based on the number of values:

select x.*
from (select val,
             count(*) as cnt,
             row_number() over (order by count(*) desc ) as seqnum,
             count(*) over () as num_vals
             count(*) over (partition by count(*)) as cnt_cnt
      from table 
      group by val
     ) x
where cnt_cnt = 1 and seqnum = 1 and num_vals > 1;

Actually, you can achieve this using the having clause and order by:

select val
from (select val, count(*) as cnt,
             count(*) over () as num_values
      from table 
      group by val
     ) v
where num_values > 1
order by cnt desc;