How to calculate the number of messages within 10 seconds before the previous one? - postgresql

Question

I have a table with messages and I need to find chats where were two or more messages in period of 10 seconds. table
id message_id time
1 1 2021.11.10 13:09:00
1 2 2021.11.10 13:09:01
1 3 2021.11.10 13:09:50
2 1 2021.11.10 15:18:00
2 2 2021.11.10 15:20:00
3 1 2021.11.12 15:00:00
3 2 2021.11.12 15:10:00
3 2 2021.11.12 15:10:10
So the result looks like
id
1
3
I can't come up with the idea how to group by a period or maybe it can be done other way?
select id
from t
group by id, ?
having count(message_id) > 1

Answer 1

You can join the table with itself, matching them on the chat id and your timeframe.
create table messages (chat_id integer,message_id integer,"time" timestamp);
insert into messages values
(1,1,'2021.11.10 13:09:00'),
(1,2,'2021.11.10 13:09:01'),
(1,3,'2021.11.10 13:09:50'),
(2,1,'2021.11.10 15:18:00'),
(2,2,'2021.11.10 15:20:00'),
(3,1,'2021.11.12 15:00:00'),
(3,2,'2021.11.12 15:10:00'),
(3,2,'2021.11.12 15:10:10');
select target_chat,
target_message,
count(*) "number of messages preceding by no more than 10 seconds"
from
(select t1.chat_id target_chat,
t1.message_id target_message,
t1.time,
t2.chat_id,
t2.message_id,
t2.time
from messages t1
inner join messages t2
on t1.chat_id=t2.chat_id
and t1.message_id<>t2.message_id
and (t2.time<=t1.time-'10 seconds'::interval and t2.time<=t1.time)) a
group by 1,2;
-- target_chat | target_message | number of messages preceding by no more than 10 seconds
---------------+----------------+---------------------------------------------------------
-- 1 | 3 | 2
-- 2 | 2 | 1
-- 3 | 2 | 2
--(3 rows)
From that you can select the records with your desired number of preceding messages.

Answer 2

this is a simple query that finds every previous value that is included in our interval
select id from test_table t where
t.time + interval '10 second' >=
(select time from test_table where id=t.id and time>t.time limit 1)
group by id;
results
id
----
1
3

Answer 3

To find rows within an period of time, you can tipically use a window function which avoids a self join on the table :
SELECT id, count(*) OVER (ORDER BY time RANGE BETWEEN CURRENT ROW AND '10 minutes' FOLLOWING)
FROM t
GROUP BY id
Then you can use this query as a sub-query if you only want the id with count(*) > 1 :
SELECT DISTINCT ON (l.id) l.id
FROM
( SELECT id, count(*) OVER (ORDER BY time RANGE BETWEEN CURRENT ROW AND '10 minutes' FOLLOWING) AS ct
FROM t
GROUP BY id
) AS l
WHERE l.ct > 1 ;