Question

Assume we have the following table:

Id   A    B
1    10   ABC
2    10   ABC
3    10   FFF
4    20   HHH

As result of a “group by A” expression I want to have the value of the B-Column that occurs most often:

select A, mostoften(B) from table group by A;

A    mostoften(B)
10   ABC
20   HHH

How do I achieve this in Oracle 10g?

Remark: in the case of a tie (when there are more than one value that occurs most often) it does not matter which value is selected.

Answer 1

select A, B
from (
  select A, B, ROW_NUMBER() OVER (PARTITION BY A ORDER BY C_B DESC) as rn
  from (
     select A, COUNT (B) as C_B, B
     from table
     group by A, B
  ) count_table
) order_table
where rn = 1;

You want the Bs with the MAX of COUNT group by A, B.