Mysql workaround for window functions

Question

I have an event table that has the following fields:

event_id
event_type 
event_time

Given a duration D and a number k<

Answer 1

Edit: Rearranged whole answer

Now I understand what you expect.

I've created such a test table on my MySQL and this seems to work:

SELECT e2.event_type FROM events e1
JOIN events e2 
    ON e1.event_time BETWEEN e2.event_time AND (e2.event_time + INTERVAL 10 MINUTE);
GROUP BY e1.event_id, e2.event_type
HAVING count(e2.event_type) >= 5

Basically, for each event you self join events with specified relative time window (from event_time to event_time + window duration), and then you group by e1's even_id to get emulated floating time window. Also we're gruping by event_type here because you want to get this field values for each window.

All you need to think through is performance. I'm not sure if it will be efficient enough for a 1M of records.

Answer 2

MySQL has no window function support, but you can use a correlated subqueries in the SELECT list to retrieve exactly one column:

SELECT
  event_id,
  event_type, 
  event_time,
  (SELECT COUNT(*) FROM events EC WHERE EC.event_type = E.event_type AND EC.event_time > E.event_time) AS subsequent_event_count
FROM
  events E
WHERE ...

Do EXPLAIN it. This is kinda the same in terms of execution logic as the CROSS APPLY in SQL Server.

Another approach is a self join:

SELECT
  E.event_id,
  E.event_type,
  E.event_time,
  COUNT(EC.event_id) AS subsequent_event_count
FROM
  events E
  LEFT JOIN events EC
    ON E.event_type = EC.event_type AND E.event_type < EC.event_type
GROUP BY
  E.event_id,
  E.event_type,
  E.event_time

Do test both approaches for performance.

You can do much more creative joins, like

EC.event_time > E.event_time AND EC.event_time < E.event_time + INTERVAL 1 DAY

Answer 3

Do CTE's work fast enough?

WITH etypes_in_range AS (
SELECT tn.event_type,
       count(1) AS num
  FROM tablename tn
 WHERE tn.event_time < time_interval_end
   AND tn.event_time > time_interval_start
 GROUP BY tn.event_type
 HAVING count(1) > 5)
SELECT count(1)
  FROM etypes_in_range

Answer 4

Notice that this lack of functionality is a thing of the past with MySQL 8 and later: https://dev.mysql.com/doc/refman/8.0/en/window-functions.html