How do you find overlapping date ranges?

Short answer: Two ranges [a,b] and [c,d] overlap when a <= d AND c <= b (for closed intervals). Self-join bookings/events with that predicate and exclude the same Id.

Sample solution

SELECT a.Id AS Id1, b.Id AS Id2
FROM Bookings a
INNER JOIN Bookings b ON a.Id < b.Id
    AND a.StartDate <= b.EndDate
    AND b.StartDate <= a.EndDate;

Clarify inclusive/exclusive end times — hotel checkout logic often uses half-open intervals.