How do I use Group By based on a Case statement in Oracle?

Question

I have an SQL-query where I use Oracle CASE to compare if a date column is less than or greater than current date. But how do I use that

Answer 1

select
(case
    when exp_date > sysdate then 1
    when exp_date <= sysdate then 2
    else 3
 end) expired, count(*)
from mytable
group by (case
    when exp_date > sysdate then 1
    when exp_date <= sysdate then 2
    else 3
 end)