-- The overlap exclusion constraint must not apply to cancelled reservations,
-- so that a cancelled slot can be re-booked by another member.

alter table public.reservations
  drop constraint no_overlapping_reservations;

alter table public.reservations
  add constraint no_overlapping_reservations
  exclude using gist (
    boat_id with =,
    tstzrange(start_time, end_time, '[)') with &&
  ) where (status <> 'cancelled');