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

Here is a solution which creates a "range" table in a sub-query and then uses this to partition the data from the main table:

SELECT DISTINCT descr
  , COUNT(*) OVER (PARTITION BY descr) n
FROM age_table INNER JOIN (
  select '1-10' descr, 1 rng_start, 10 rng_stop from dual
  union (
  select '11-20', 11, 20 from dual
  ) union (
  select '20+', 21, null from dual
)) ON age BETWEEN nvl(rng_start, age) AND nvl(rng_stop, age)
ORDER BY descr;