Question

I have an events based table that I would like to produce a query, by minute for the number of events that were occuring.

For example, I have an event table like:

CREATE TABLE events (
     session_id  TEXT,
     event       TEXT,
     time_stamp  DATETIME
)

Which I have transformed into the following type of table:

CREATE TABLE sessions (
     session_id    TEXT,
     start_ts      DATETIME,
     end_ts        DATETIME,
     duration      INTEGER
);

Now I want to create a query that would group the sessions by a count of those that were active during a particular minute. Where I would essentially get back something like:

TIME_INTERVAL ACTIVE_SESSIONS
------------- ---------------
18:00         1
18:01         5
18:02         3
18:03         0
18:04         2

Answer 1

Ok, I think I got more what I wanted. It doesn’t account for intervals that are empty, but it is good enough for what I need.

select strftime('%Y-%m-%dT%H:%M:00.000',start_ts) TIME_INTERVAL, 
    (select count(session_id) 
      from sessions s2 
      where strftime('%Y-%m-%dT%H:%M:00.000',s1.start_ts) between s2.start_ts and s2.end_ts) ACTIVE_SESSIONS
   from sessions s1
   group by strftime('%Y-%m-%dT%H:%M:00.000',start_ts);

This will generate a row per minute for the period that the data covers with a count for the number of sessions that were had started (start_ts) but hadn’t finished (end_ts).