Question

I’m trying to count entries grouped per hour.
I’ve found some useful info inform on different sites and here on: MySQL Group By Hours

But the result is not what I’ve expected.
With the following code I get:

SELECT   CONCAT(Hour, ':00-', Hour+1, ':00') AS Hours,
     COUNT(`usage_time`) AS `usage` FROM `usage`
  RIGHT JOIN (
                   SELECT  0 AS Hour
         UNION ALL SELECT  1 UNION ALL SELECT  2 UNION ALL SELECT  3
         UNION ALL SELECT  4 UNION ALL SELECT  5 UNION ALL SELECT  6
         UNION ALL SELECT  7 UNION ALL SELECT  8 UNION ALL SELECT  9
         UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12
         UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL SELECT 15
         UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL SELECT 18
         UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21
         UNION ALL SELECT 22 UNION ALL SELECT 23
  )      AS AllHours ON HOUR(`usage_time`) = Hour

WHERE `usage_function` LIKE 'PlayedWholeSong' AND `usage_date` = DATE_SUB(CURDATE(), INTERVAL 0 DAY) OR `usage_time` IS NULL
GROUP BY Hour
ORDER BY Hour

Result:

Hours       usage
2:00-3:00   0
4:00-5:00   6
6:00-7:00   2
8:00-9:00   3
9:00-10:00  20
10:00-11:00 1
14:00-15:00 14
15:00-16:00 1
16:00-17:00 32
17:00-18:00 10

As these are entry’s from today, I don’t have any entries after 19:00.
Also I don’t see an entry from 00:00 – 01:00, 03:00 – 04:00 and several others are missing.
But I do want to show a list with every 24 hour and the result, even if there’s nothing.
String thing is the result shows a 0 between 02:00 – 03:00.
I’ve learned a lot today about mysql, but nothing that solves my issue.

I hope you can learn me something, doesn’t have to be code, a direction would be great.

Answer 1

I prefer LEFT JOIN over RIGHT JOIN personally. That way you can add your WHERE criteria in your JOIN and it won’t constrict your results. Try this:

SELECT   CONCAT(Hour, ':00-', Hour+1, ':00') AS Hours,
     COUNT(`usage_time`) AS `usage` 
FROM 
   (
         SELECT  0 AS Hour
         UNION ALL SELECT  1 UNION ALL SELECT  2 UNION ALL SELECT  3
         UNION ALL SELECT  4 UNION ALL SELECT  5 UNION ALL SELECT  6
         UNION ALL SELECT  7 UNION ALL SELECT  8 UNION ALL SELECT  9
         UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12
         UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL SELECT 15
         UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL SELECT 18
         UNION ALL SELECT 19 UNION ALL SELECT 20 UNION ALL SELECT 21
         UNION ALL SELECT 22 UNION ALL SELECT 23
  )      AS AllHours 
      LEFT JOIN `usage` ON HOUR(`usage_time`) = Hour 
           AND `usage_function` LIKE 'PlayedWholeSong' 
           AND `usage_date` = DATE_SUB(CURDATE(), INTERVAL 0 DAY) 
GROUP BY Hour
ORDER BY Hour

Here is a simplified SQL Fiddle.

Good luck.