--
--
-- Forbidding gaps and overlaps:
--
--
SELECT  room_id, range_agg(booked_during)
FROM    reservations
WHERE   room_id = 1
GROUP BY room_id
ORDER BY room_id;
ERROR:  range_agg: gap detected between lastRange and currentRange
SELECT  room_id, range_agg(booked_during)
FROM    reservations
WHERE   room_id = 6
GROUP BY room_id
ORDER BY room_id;
ERROR:  range_agg: overlap detected between lastRange and currentRange
SELECT  room_id, range_agg(booked_during)
FROM    reservations
WHERE   room_id NOT IN (1, 6)
GROUP BY room_id
ORDER BY room_id;
 room_id |        range_agg        
---------+-------------------------
       2 | [07-01-2018,07-03-2018)
       3 | 
       4 | 
       5 | [07-01-2018,07-03-2018)
       7 | [07-01-2018,07-14-2018)
(5 rows)

--
--
-- Obeying discrete base types:
--
--
SELECT	range_agg(r)
FROM		(VALUES 
  (int4range( 0,  9, '[]')),
  (int4range(10, 19, '[]'))
) t(r);
 range_agg 
-----------
 [0,20)
(1 row)