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CREATE TABLE usersessions (userid int, starttime timestamp, endtime timestamp); INSERT INTO usersessions (userid, starttime, endtime) VALUES (1, '01-Oct-19 6:00:00 AM', '01-Oct-19 11:10:00 AM'), (2, '01-Oct-19 11:00:00 AM', '01-Oct-19 4:00:00 PM'), (3, '01-Oct-19 10:30:00 AM', '01-Oct-19 4:00:00 PM'), (4, '2019-10-02 06:00:00', '2019-10-02 11:30:00'), -- does not overlap (5, '2019-10-02 06:00:00', '2019-10-02 11:30:01'), -- overlaps (6, '2019-10-02 11:00:00', '2019-10-02 16:00:00'), (7, '2019-10-02 10:30:00', '2019-10-02 16:00:00') ;
7 rows affected
-- calculating for all of Oct 2019 WITH range AS (SELECT timestamp '2019-10-01' AS start_ts -- incl. lower bound , timestamp '2019-11-01' AS end_ts) -- excl. upper bound , cte AS ( SELECT userid, starttime -- default to current timestamp if NULL , COALESCE(endtime, localtimestamp) - interval '30 min' AS endtime FROM usersessions, range r WHERE starttime < r.end_ts -- count overlaps *starting* in outer time range AND (endtime >= r.start_ts + interval '30 min' OR endtime IS NULL) ) , ct AS ( SELECT ts, sum(ct) OVER (ORDER BY ts, ct) AS session_ct FROM ( SELECT endtime AS ts, -1 AS ct FROM cte UNION ALL SELECT starttime , +1 FROM cte ) sub ) SELECT ts::date, max(session_ct) AS max_concurrent_sessions FROM ct, range r WHERE ts >= r.start_ts AND ts < r.end_ts -- crop outer time range GROUP BY ts::date ORDER BY 1;
ts
max_concurrent_sessions
2019-10-01
2
2019-10-02
3