MySQL Group By Hours

问题:

I'm trying to get a report from my history table by hourly usage. history table is;

CREATE TABLE IF NOT EXISTS `history` ( `history_id` int(11) unsigned NOT NULL AUTO_INCREMENT, `user_id` int(11) unsigned NOT NULL DEFAULT '0', `created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, PRIMARY KEY (`history_id`), KEY `user_id` (`user_id`), KEY `created` (`created`) ) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ; 

I want to group by HOUR and COUNT all records in a given date range.

Hours            |    Usage ------------------------------------ 00:00-01:00      |      5 01:00-02:00      |      9 02:00-03:00      |      0 (or NULL) 03:00-04:00      |      20 ... ... ... 22:00-23:00      |      11 23:00-00:00      |      1 

I used a query something like this but it doesn't display all hours.

SELECT   CASE    WHEN HOUR(created) BETWEEN 0 AND 1 THEN '00:00 - 01:00'   WHEN HOUR(created) BETWEEN 1 AND 2 THEN '01:00 - 02:00'   WHEN HOUR(created) BETWEEN 2 AND 3 THEN '02:00 - 03:00'   WHEN HOUR(created) BETWEEN 3 AND 4 THEN '03:00 - 04:00'   WHEN HOUR(created) BETWEEN 4 AND 5 THEN '04:00 - 05:00'   WHEN HOUR(created) BETWEEN 5 AND 6 THEN '05:00 - 06:00'   WHEN HOUR(created) BETWEEN 6 AND 7 THEN '06:00 - 07:00'   WHEN HOUR(created) BETWEEN 7 AND 8 THEN '07:00 - 08:00'   WHEN HOUR(created) BETWEEN 8 AND 9 THEN '08:00 - 09:00'   WHEN HOUR(created) BETWEEN 9 AND 10 THEN '09:00 - 10:00'   WHEN HOUR(created) BETWEEN 10 AND 11 THEN '10:00 - 11:00'   WHEN HOUR(created) BETWEEN 11 AND 12 THEN '11:00 - 12:00'   WHEN HOUR(created) BETWEEN 12 AND 13 THEN '12:00 - 13:00'   WHEN HOUR(created) BETWEEN 13 AND 14 THEN '13:00 - 14:00'   WHEN HOUR(created) BETWEEN 14 AND 15 THEN '14:00 - 15:00'   WHEN HOUR(created) BETWEEN 15 AND 16 THEN '15:00 - 16:00'   WHEN HOUR(created) BETWEEN 16 AND 17 THEN '16:00 - 17:00'   WHEN HOUR(created) BETWEEN 17 AND 18 THEN '17:00 - 18:00'   WHEN HOUR(created) BETWEEN 18 AND 19 THEN '18:00 - 19:00'   WHEN HOUR(created) BETWEEN 19 AND 20 THEN '19:00 - 20:00'   WHEN HOUR(created) BETWEEN 20 AND 21 THEN '20:00 - 21:00'   WHEN HOUR(created) BETWEEN 21 AND 22 THEN '21:00 - 23:00'   WHEN HOUR(created) BETWEEN 22 AND 23 THEN '22:00 - 23:00'   WHEN HOUR(created) BETWEEN 23 AND 24 THEN '23:00 - 00:00' END AS `Hours`,  COUNT(*) AS `usage` FROM history WHERE (created BETWEEN '2012-02-07' AND NOW()) GROUP BY    CASE      WHEN HOUR(created) BETWEEN 0 AND 1 THEN 1     WHEN HOUR(created) BETWEEN 1 AND 2 THEN 2     WHEN HOUR(created) BETWEEN 2 AND 3 THEN 3     WHEN HOUR(created) BETWEEN 3 AND 4 THEN 4     WHEN HOUR(created) BETWEEN 4 AND 5 THEN 5     WHEN HOUR(created) BETWEEN 5 AND 6 THEN 6     WHEN HOUR(created) BETWEEN 6 AND 7 THEN 7     WHEN HOUR(created) BETWEEN 7 AND 8 THEN 8     WHEN HOUR(created) BETWEEN 8 AND 9 THEN 9     WHEN HOUR(created) BETWEEN 9 AND 10 THEN 10     WHEN HOUR(created) BETWEEN 10 AND 11 THEN 11     WHEN HOUR(created) BETWEEN 11 AND 12 THEN 12     WHEN HOUR(created) BETWEEN 12 AND 13 THEN 13     WHEN HOUR(created) BETWEEN 13 AND 14 THEN 14     WHEN HOUR(created) BETWEEN 14 AND 15 THEN 15     WHEN HOUR(created) BETWEEN 15 AND 16 THEN 16     WHEN HOUR(created) BETWEEN 16 AND 17 THEN 17     WHEN HOUR(created) BETWEEN 17 AND 18 THEN 18     WHEN HOUR(created) BETWEEN 18 AND 19 THEN 19     WHEN HOUR(created) BETWEEN 19 AND 20 THEN 20     WHEN HOUR(created) BETWEEN 20 AND 21 THEN 21     WHEN HOUR(created) BETWEEN 21 AND 22 THEN 22     WHEN HOUR(created) BETWEEN 22 AND 23 THEN 23     WHEN HOUR(created) BETWEEN 23 AND 24 THEN 24 END 

It displays only if there are any records.

Hours            |    Usage ------------------------------------ 00:00-01:00      |      5 01:00-02:00      |      9 23:00-00:00      |      1 

回答1:

Your existing query can be reduced to:

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) 

To display every hour, including those for which there is no data, you need to outer join with a table containing all the hours for which you want data. You can build such a table in your query using 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 

However, the treatment of groups for which no data exists is really a matter for business logic that's best placed in your data access layer rather than in the database itself: indeed it should be trivial for your application to use a zero value whenever an hour is absent.

回答2:

Given a table Log with columns ts and value, the following will give the hourly average for the last 24 hours (assuming each hour has at least one row).

SELECT      FROM_UNIXTIME( TRUNCATE( UNIX_TIMESTAMP( `ts` )/3600, 0 ) * 3600 ) as h,     AVG( `value` ) as v,     COUNT( * ) as q FROM      Log GROUP BY     h ORDER BY     h desc LIMIT     24 

The column ts can be a timestamp or datetime column while value is anything that AVG() will accept.

文章来源: MySQL Group By Hours