Oracle: how to “group by” over a range?

Question

If I have a table like this:

pkey   age
----   ---
   1     8
   2     5
   3    12
   4    12
   5    22

I can \"group by\" to get a count

Answer 1

My approach:

select range, count(1) from (
select case 
  when age < 5 then '0-4' 
  when age < 10 then '5-9' 
  when age < 15 then '10-14' 
  when age < 20 then '15-20' 
  when age < 30 then '21-30' 
  when age < 40 then '31-40' 
  when age < 50 then '41-50' 
  else                '51+' 
end 
as range from
(select round(extract(day from feedback_update_time - feedback_time), 1) as age
from txn_history
) ) group by range  

• I have flexibility in defining the ranges
• I do not repeat the ranges in select and group clauses
• but some one please tell me, how to order them by magnitude!