sql-按范围分组以包括没有值的范围

Question

假设有一个与此问题类似的情况。我想得到以下结果：

score range  | number of occurrences
-------------------------------------
   0-9       |        11
  10-19      |        14
  20-29      |         3
   ...       |       ...

我可以使用选定的答案作为解决方案：

select t.range as [score range], count(*) as [number of occurences]
from (
  select case  
    when score between 0 and 9 then ' 0- 9'
    when score between 10 and 19 then '10-19'
    else '20-99' end as range
  from scores) t
group by t.range

我如何确保即使在该范围内没有任何结果，也将显示30-39的分数范围？

Answer 1

尝试以下查询（也在SQL Fiddle上）：

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;

编辑：

您可以通过将参数更改为轻松调整范围generate_series()。可以使用以下构造来确保ranges始终覆盖您的分数：

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))

对于rangesCTE。