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

Answer 1

Try:

select to_char(floor(age/10) * 10) || '-' 
|| to_char(ceil(age/10) * 10 - 1)) as age, 
count(*) as n from tbl group by floor(age/10);

Answer 2

add an age_range table and an age_range_id field to your table and group by that instead.

// excuse the DDL but you should get the idea

create table age_range(
age_range_id tinyint unsigned not null primary key,
name varchar(255) not null);

insert into age_range values 
(1, '18-24'),(2, '25-34'),(3, '35-44'),(4, '45-54'),(5, '55-64');

// again excuse the DML but you should get the idea

select
 count(*) as counter, p.age_range_id, ar.name
from
  person p
inner join age_range ar on p.age_range_id = ar.age_range_id
group by
  p.age_range_id, ar.name order by counter desc;

You can refine this idea if you like - add from_age to_age columns in the age_range table etc - but i'll leave that to you.

hope this helps :)

Answer 3

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;

Answer 4

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

Answer 5

If using Oracle 9i+, you might be able to use the NTILE analytic function:

WITH tiles AS (
  SELECT t.age,
         NTILE(3) OVER (ORDER BY t.age) AS tile
    FROM TABLE t)
  SELECT MIN(t.age) AS min_age,
         MAX(t.age) AS max_age,
         COUNT(t.tile) As n
    FROM tiles t
GROUP BY t.tile

The caveat to NTILE is that you can only specify the number of partitions, not the break points themselves. So you need to specify a number that is appropriate. IE: With 100 rows, NTILE(4) will allot 25 rows to each of the four buckets/partitions. You can not nest analytic functions, so you'd have to layer them using subqueries/subquery factoring to get desired granularity. Otherwise, use:

  SELECT CASE t.age
           WHEN BETWEEN 1 AND 10 THEN '1-10' 
           WHEN BETWEEN 11 AND 20 THEN '11-20' 
           ELSE '21+' 
         END AS age, 
         COUNT(*) AS n
    FROM TABLE t
GROUP BY CASE t.age
           WHEN BETWEEN 1 AND 10 THEN '1-10' 
           WHEN BETWEEN 11 AND 20 THEN '11-20' 
           ELSE '21+' 
         END