sql - group by in ranges to include ranges without values

Question

Suppose a scenario similar to this question. I want to get the following results:

score range  | number of occurrences
-------------------------------------
   0         


        

Answer 1

Actually, the simplest solution is this (for 2 digit numbers):

select substr(rssi::text, 0, 2) || '0-' || substr(rssi::text, 0, 2) || '9' as range, count(*)
from sensor_stations
group by substr(rssi::text, 0, 2)
order by count(*) desc;

The output will be something like this:

 range | count 
-------+-------
 10-19 |  3414
 30-39 |  1363
 20-29 |  1269
 40-49 |   769
 50-59 |   294
 60-69 |   106
 70-79 |     5
(7 rows)