Peak visit counts by datetime period

from the Artful Common Queries page


You have a visits table (id int, start datetime, end datetime), and you wish to track peak visit counts. A simple solution is to self-join on non-matching IDs and overlapping visit times, group by ID, then order by the resulting counts:
SELECT a.id,group_concat(b.id) as Overlaps, count(b.id)+1 as OverlapCount
FROM visits a
JOIN visits b on a.id < b.id and a.start < b.end and b.start < a.end
GROUP BY a.id
ORDER BY OverlapCount DESC;

Last updated 22 May 2009




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