Define Sessions not only with time limit - sql

Question

I've been trying to group an events-like table (user, action, event_time) into sessions .
But the common "idle time" approach is not enough.
I need to check if the user was idle for more than an period X of time (ok), BUT if the user started the game, then it will very likely be idle for a long time and every action between start game and end game, regardless of the time interval, should not be considered a new session. But when the game finishes, a new session shows up:
For example (idle time 5 min)
| action | user | event_at | new_session? (desired output) |
|---------------|------|--------------|-------------------------------|
| random1 | 1 | 1 sec | 1 |
| random3 | 1 | 30 sec | 0 |
| random4 | 1 | 6:00 min | 1 |
| random5 | 1 | 7:00 min | 0 |
| game_started | 1 | 7:30 min | 0 |
| random2 | 1 | 20:00 min | 0 |
| random5 | 1 | 27:00 min | 0 |
| game_finished | 1 | 35:00 min | 0 |
| random5 | 1 | 35:30 min | 1 |
The problem are those random actions between the game_start and game_finish. I cannot tell SQL to ignore them and not count them as a new session when using the idle time logic (- that is needed for the part not between start and finish).
in "proper" programming language I could just add a flag after the "for" or "while" finds "game started" and tell it to ignore anything until "game_finished" is found. But in SQL this is simply not that easy, even using an auxiliary column.
Any Ideas ?
Thanks in advance!

Answer 1

Identify the games first, then use lag() for the session start:
select t.*,
(case when in_game > 0 and
(lag(in_game) over (order by time) is null or
lag(in_game) over (order by time) = 0
)
then 1
when in_game = 0 and
(lag(time) over (partition by in_game order by time) is null or
lag(time) over (partition by in_game order by time) < time - interval '5 minute'
)
then 1
else 0
end) as new_session
from (select t.*,
sum(case when action = 'game_start' then 1
when action = 'game_end' then -1
end) over (order by time) as in_game
from t
) t;
This does not handle every edge case. For instance, this version does not handle nested games. It might also be tricky with games right next to each other. But I think it does do what you want.