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 CASE-statement in a GROUP BY-statement? I would like to count the records in each case.

E.g.

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

But I get an error when trying this: ORA-00904. Any suggestions?

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)