In SQL, how can you “group by” in ranges?

Question

Suppose I have a table with a numeric column (lets call it "score").

I'd like to generate a table of counts, that shows how many times scores appeared in each range.

For example:

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

In this example there were 11 rows with scores in the range of 0 to 9, 14 rows with scores in the range of 10 to 19, and 3 rows with scores in the range 20-29.

Is there an easy way to set this up? What do you recommend?

Answer 1

Because the column being sorted on (Range) is a string, string/word sorting is used instead of numeric sorting.

As long as the strings have zeros to pad out the number lengths the sorting should still be semantically correct:

SELECT t.range AS ScoreRange,
       COUNT(*) AS NumberOfOccurrences
  FROM (SELECT CASE
                    WHEN score BETWEEN 0 AND 9 THEN '00-09'
                    WHEN score BETWEEN 10 AND 19 THEN '10-19'
                    ELSE '20-99'
               END AS Range
          FROM Scores) t
 GROUP BY t.Range

If the range is mixed, simply pad an extra zero:

SELECT t.range AS ScoreRange,
       COUNT(*) AS NumberOfOccurrences
  FROM (SELECT CASE
                    WHEN score BETWEEN 0 AND 9 THEN '000-009'
                    WHEN score BETWEEN 10 AND 19 THEN '010-019'
                    WHEN score BETWEEN 20 AND 99 THEN '020-099'
                    ELSE '100-999'
               END AS Range
          FROM Scores) t
 GROUP BY t.Range

Answer 2

declare @RangeWidth int

set @RangeWidth = 10

select
   Floor(Score/@RangeWidth) as LowerBound,
   Floor(Score/@RangeWidth)+@RangeWidth as UpperBound,
   Count(*)
From
   ScoreTable
group by
   Floor(Score/@RangeWidth)

Answer 3

I see answers here that won't work in SQL Server's syntax. I would use:

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'
    when score between 20 and 29 then '20-29'
    ...
    else '90-99' end as range
  from scores) t
group by t.range

EDIT: see comments

Answer 4

I would do this a little differently so that it scales without having to define every case:

select t.range as [score range], count(*) as [number of occurences]
from (
  select FLOOR(score/10) as range
  from scores) t
group by t.range

Not tested, but you get the idea...

Answer 5

In postgres (where || is the string concatenation operator):

select (score/10)*10 || '-' || (score/10)*10+9 as scorerange, count(*)
from scores
group by score/10
order by 1

gives:

 scorerange | count 
------------+-------
 0-9        |    11
 10-19      |    14
 20-29      |     3
 30-39      |     2

Answer 6

select t.blah 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'
    when score between 20 and 29 then '20-29'
    ...
    else '90-99' end as blah
  from scores) t
group by t.blah

Make sure you use a word other than 'range' if you are in MySQL, or you will get an error for running the above example.