Question

Lets say, i have the following table

| start               | end                 | activity
+---------------------+---------------------+---------
| 2010-07-26 09:10:00 | 2010-07-26 09:21:00 | 6
| 2010-07-26 09:35:00 | 2010-07-26 09:47:00 | 5
| 2010-07-26 10:05:00 | 2010-07-26 10:45:00 | 5
| 2010-07-26 10:50:00 | 2010-07-26 11:22:00 | 6
| 2010-07-26 13:15:00 | 2010-07-26 13:43:00 | 7
| 2010-07-26 14:12:00 | 2010-07-26 14:55:00 | 2

I want to combine the small time spans, getting the average minutes with activity per hour. Something like that:

| start               | minutes_activity    | avg_activity
+---------------------+---------------------+---------
| 2010-07-26 09:00:00 | 42                  | {avg value}
| 2010-07-26 10:00:00 | 50                  | {avg value}
| 2010-07-26 11:00:00 | 22                  | {avg value}
| 2010-07-26 13:00:00 | 28                  | {avg value}
| 2010-07-26 14:00:00 | 43                  | {avg value}

Note that some records can have activity minutes in two hours, i.e 10:50:00 – 11:22:00. In this case, 10 minutes should be added to 10:00 and 22 minutes to 11:00.

A solution, be it MySql, PHP or both is appreciated.

Thank you advance.

Answer 1

Let’s assume that your table is named records and that your time intervals don’t span through more than two hours:

SELECT DISTINCT(CONCAT(date,' ',IF(LENGTH(hour)=1, CONCAT('0',hour), hour), ':00:00')) AS start,
       SUM(minutes) AS minutes_activity,
       FORMAT(avg(activity),0) AS avg_activity
FROM (
      SELECT date, hour, minutes, activity
      FROM (
            SELECT DATE(start) AS date,
                   HOUR(ADDDATE(start, INTERVAL 1 HOUR)) AS hour,
                   IF(HOUR(start) < HOUR(end), MINUTE(end), 0) AS minutes,
                   activity AS activity
            FROM records
            HAVING minutes>0
           ) t1
      UNION (
             SELECT DATE(ADDDATE(start, INTERVAL 1 DAY)) AS date,
                    HOUR(ADDDATE(start, INTERVAL 1 HOUR)) AS hour,
                    IF(HOUR(start) > HOUR(end), MINUTE(end), 0) AS minutes,
                    activity AS activity
             FROM records
             HAVING minutes>0
                    AND hour=0
            )
      UNION (
             SELECT DATE(start) AS date,
                    HOUR(start) AS hour,
                    IF(HOUR(start) < HOUR(end),
                       (60 - MINUTE(start)),
                       IF(
                          DATE(start) < DATE(end),
                          (60 - MINUTE(start)),
                          (MINUTE(end) - MINUTE(start))
                       )
                    ) AS minutes,
                    activity AS activity
             FROM records
            )
      ORDER BY date ASC, hour ASC) t2
GROUP BY CONCAT(date,' ',IF(LENGTH(hour)=1, CONCAT('0',hour), hour), ':00:00');

… however, if you have an interval that goes from e.g. 2010-10-08 01:30:00 to 2010-10-08 03:13:00, a (not so) simple SQL query won’t do it.