Sessions Running Concurrently

SQLHardSenior levelPinterest~15 min

Problem

**[Asked at Pinterest]**

Pinterest monitors server load by tracking overlapping user sessions.
Two sessions overlap if one starts before the other ends.

For each session, count how many **other** sessions were running at the
same time (i.e., their time intervals overlap with this session's interval).

Return `session_id` and `concurrent_count`, ordered by session_id.

Example rows — the live problem includes the full dataset.

sessions

session_id	user_id	session_start	session_end

Your answer should return 5 rows with the columns session_id, concurrent_count.

SELECT *
FROM sessions;

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