MySQL: select entries with a certain count within a certain period - mysql

Question

I have a MySQL table with a datetime row. How can I find all groups with at least 5 entries within 10 minutes?
My only idea is to write a program (in whatever language) and loop over the timestamps, check always 5 (..) successive entries, calculate the time span between the last and the first and check whether it is below the limit.
Can this be done using a single SQL query too?
(The scenario is is simplified and the numbers are just examples.)
As requested, here comes an example:
id | timestamp | other_column
---|---------------------|-------------
3 | 2017-01-01 11:00:00 | thank
2 | 2017-01-01 11:01:00 | you
1 | 2017-01-01 11:02:00 | for
* 6 | 2017-01-01 11:20:00 | your
* 5 | 2017-01-01 11:21:00 | efforts
* 4 | 2017-01-01 11:22:00 | to
* 7 | 2017-01-01 11:23:00 | help
* 8 | 2017-01-01 11:24:00 | me
9 | 2017-01-01 11:40:00 | :
10 | 2017-01-01 11:41:00 | )
If the count limit is 5 and the timespan limit is 10 minutes, I'd like to get the entries marked with "*". The "id" column is the primary key of the table, but the order is not always the order of the timestamps. The "other_column" is used for a where clause. The table has about 1 million entries.

Answer 1

Try to break this down logically. Sorry for the psuedo code bits, I'm a little short on time.
select t1.id, t1.timestamp, t2.timestamp
from yourtable t1
inner join yourtable t2 on t2.timestamp >= t1.timestamp and t2.timestamp < (t1.timestamp + 20 minutes)
(plus 20 minutes won't work as is, use appropriate add function)
So this will give you a relatively giant list of all ID's joined to any other id's within a 20 minute time interval (including one row for itself). (add, I'm only picking out the first row of the group at this point, easier just to grab the 'header row' here by this timestamp plus 20 minutes and worry about the rest in the next step) If we group by the ID and time, we get a count of how many rows were within 20 minutes:
select id, t1.timestamp, count(1)
from yourtable t1
inner join yourtable t2 on t2.timestamp >= t1.timestamp and t2.timestamp < (t1.timestamp + 20 minutes)
group by id, t1.timestamp
having count(1) > 4
This will now give you a list of all the ID's and it's timestamp that has itself and 4 other records or more within 20 minutes away from that timestamp. Now it depends on how you want to group from here, if you want each of the 5 lines, we can call the query above a subquery and join it back to the main table to get the rows you want returned.
select t3.*
from
(select id, t1.timestamp, count(1)
from yourtable t1
inner join yourtable t2
on t2.timestamp >= t1.timestamp and t2.timestamp < (t1.timestamp + 20 minutes)
group by id, t1.timestamp
having count(1) > 4) a
inner join yourtable t3 on t3.timestamp >= a.timestamp and t3.timestamp < (a.timestamp + 20 minutes)
And that should give you ID 4-8 and it's info returned (order as you see fit).
My apologies that I don't have the time to test, but the logic should work.