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 of each age.

select age,count(*) n from tbl group by age;
age  n
---  -
  5  1
  8  1
 12  2
 22  1

What query can I use to group by age ranges?

  age  n
-----  -
 1-10  2
11-20  2
20+    1

I'm on 10gR2, but I'd be interested in any 11g-specific approaches as well.

Answer 1

SELECT CASE 
         WHEN age <= 10 THEN '1-10' 
         WHEN age <= 20 THEN '11-20' 
         ELSE '21+' 
       END AS age, 
       COUNT(*) AS n
FROM age
GROUP BY CASE 
           WHEN age <= 10 THEN '1-10' 
           WHEN age <= 20 THEN '11-20' 
           ELSE '21+' 
         END