Grupa Mysql W odstępach 24-godzinnych

Spróbuj tego:

SELECT MIN(creation_date), MAX(creation_date), COUNT(*) AS Occurrences 
FROM test
GROUP BY DATE(DATE_SUB(creation_date, INTERVAL 19 HOUR))

Demo pracy:http://sqlfiddle.com/#!2/aa7583/6

Do formatowania użyj tego:

SELECT CONCAT( CONCAT(DATE(DATE_SUB(creation_date, INTERVAL 19 HOUR)),' 19:00:00') , ' - ' , CONCAT(DATE(DATE_ADD(creation_date, INTERVAL 5 HOUR)), ' 18:59:00') ) AS Interval, COUNT(*) AS Occurrences 
FROM test
GROUP BY DATE(DATE_SUB(creation_date, INTERVAL 19 HOUR))