SQL- Return rows after nth occurrence of event per user

Question

I'm using postgreSQL 8.0 and I have a table with user_id, timestamp, and event_id.

How can I return the rows (or row) after the 4th occurrence of event_id = someID per user?

|---------------------|--------------------|------------------|
|      user_id        |     timestamp      |     event_id     |
|---------------------|--------------------|------------------|
|          1          |  2020-04-02 12:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 13:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 14:00  |        99        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 15:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 16:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 17:00  |        11        |
|---------------------|--------------------|------------------|
|          2          |  2020-04-02 17:00  |        11        |
|---------------------|--------------------|------------------|

Ie if event_id = 11, I would only want the last row in the table above.

Answer 1

sorry to be asking about such an old version of Postgres, here is an answer that worked:

WITH EventOrdered AS(
  SELECT 
    EventTypeId
    , UserId
    , Timestamp
    , ROW_NUMBER() OVER (PARTITION BY EventTypeId, UserId ORDER BY Timestamp ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) ROW_NO
  FROM Event),
FourthEvent AS (
  SELECT DISTINCT
    UserID
  , FIRST_VALUE(TimeStamp) OVER (PARTITION BY UserId ORDER BY Timestamp) FirstFourthEventTimestamp
  FROM EventOrdered
  WHERE ROW_NO = 4)
SELECT e.*
FROM Event e
JOIN FourthEvent ffe
  ON e.UserId = ffe.UserId
  AND e.Timestamp > ffe.FirstFourthEventTimestamp
ORDER BY e.UserId, e.Timestamp

Answer 2

You can use window functions:

select *
from (
    select t.*, row_number() over(partition by user_id, event_id order by timestamp) rn
    from mytable t
) t
where rn > 4

Here is a little trick that removes the row number from the result:

select (t).*
from (
    select t, row_number() over(partition by user_id, event_id order by timestamp) rn
    from mytable t
) x
where rn > 4

Answer 3

You can use a cumulative count. This version includes the 4th occurrence:

select t.*
from (select t.*,
             count(*) filter (where event_id = 11) over (partition by user_id order by timestamp) as event_11_cnt
      from t
     ) t
where event_11_cnt >= 4;

The filter has been valid Postgres syntax for a long time, but instead, you can use:

select t.*
from (select t.*,
             sum( (event_id = 11)::int ) over (partition by user_id order by timestamp) as event_11_cnt
      from t
     ) t
where event_11_cnt >= 4;

This version does not:

where event_11_cnt > 4 or (event_11_cnt = 4 and event_id <> 11)

An alternative method:

select t.*
from t
where t.timestamp > (select t2.timestamp
                     from t t2
                     where t2.user_id = t.user_id and
                           t2.event_id = 11
                     order by t2.timestamp
                     limit 1 offset 3
                    );