MySQL-gruppe efter timer

Din eksisterende forespørgsel kan reduceres til:

SELECT   CONCAT(HOUR(created), ':00-', HOUR(created)+1, ':00') AS Hours
  ,      COUNT(*) AS `usage`
FROM     history
WHERE    created BETWEEN '2012-02-07' AND NOW()
GROUP BY HOUR(created)

For at vise hver time, inklusive dem, der ikke er data for, skal du outer join med en tabel, der indeholder alle de timer, du ønsker data for. Du kan bygge en sådan tabel i din forespørgsel ved hjælp af UNION :

SELECT   CONCAT(Hour, ':00-', Hour+1, ':00') AS Hours
  ,      COUNT(created) AS `usage`
FROM     history
  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(created) = Hour
WHERE    created BETWEEN '2012-02-07' AND NOW() OR created IS NULL
GROUP BY Hour
ORDER BY Hour

Men behandlingen af ​​grupper, for hvilke der ikke eksisterer data, er virkelig et spørgsmål om forretningslogik, der bedst placeres i dit dataadgangslag frem for i selve databasen:det burde faktisk være trivielt for din applikation at bruge en nulværdi, når en time er fraværende.