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

Try this query (also on SQL Fiddle):

WITH ranges AS (
    SELECT (ten*10)::text||'-'||(ten*10+9)::text AS range,
           ten*10 AS r_min, ten*10+9 AS r_max
      FROM generate_series(0,9) AS t(ten))
SELECT r.range, count(s.*)
  FROM ranges r
  LEFT JOIN scores s ON s.score BETWEEN r.r_min AND r.r_max
 GROUP BY r.range
 ORDER BY r.range;

---

EDIT:

You can easily adjust the range by changing parameters to generate_series(). It is possible to use the following construct to make sure ranges will always cover your scores:

SELECT (ten*10)::text||'-'||(ten*10+9)::text AS range,
       ten*10 AS r_min, ten*10+9 AS r_max
  FROM generate_series(0,(SELECT max(score)/10 FROM scores)) AS t(ten))

for the ranges CTE.