Mysql timestampdiff sum between overlapped intervals - mysql

Question

I have the following table structure:
+----+---------------------+---------------------+
| id | created_at | closed |
+----+---------------------+---------------------+
| 1 | 2017-04-03 04:00:00 | 2017-04-03 04:30:00 |
| 2 | 2017-04-03 04:25:00 | 2017-04-03 04:35:00 |
+----+---------------------+---------------------+
In my real SQL query I use timestampdiff to clacualte the diffirence between two dates in timestap field. There is no problem if the ctreated_at and closed_at of all records start in diffirent time intervals, so I would able to get time consumed for all rows as follows:
SELECT SUM(timestampdiff(SECOND, created_at, closed_at)) as TotalTime FROM table
My problem is like the shown table above, the time interval crossing. The above query will result 900 but it I should have 600
I have tried something like:
SELECT timestampdiff(
MINUTE,
a.created_at,
(SELECT max(b.closed) from times as b WHERE b.created_at < a.closed)
) as periods
FROM `times` as a
The result is:
+---------+
| periods |
+---------+
| 35 |
| 10 |
+---------+
Here I want only the first result whuch represnts the net time of the overlapped periods. Using MAX with the previous query should returns the first record but it will lead to neglect any other periods groups added in the futere supposed the table becomes:
+----+---------------------+---------------------+
| id | created_at | closed |
+----+---------------------+---------------------+
| 1 | 2017-04-03 04:00:00 | 2017-04-03 04:30:00 |
| 2 | 2017-04-03 04:25:00 | 2017-04-03 04:35:00 |
| 3 | 2017-04-03 05:00:00 | 2017-04-03 05:15:00 |
+----+---------------------+---------------------+
the above query returns:
+---------+
| periods |
+---------+
| 35 |
| 10 |
| 15 |
+---------+
Again here I don't want the second record because it describes its period which is previously counted in the first record. Indeed I don't know does it possible in MySQL to get (for the example above) only two records or even three records but the second is null, 0, negative value, etc to be distinguished among other really values.

Answer 1

You need to do group by the time on hourly basis and the take difference time for of max.
SELECT max(timestampdiff(
MINUTE,
a.created_at,closed) as periods
FROM `times` as a group by hour(created_at)
Now you will get result as per ur requirement.