I am trying to find a row with has null value as foreign key but all the columns return no rows

Question

I am trying to find the details of villas that have never been booked. However my query is returning no values just the column names.

Table insertion

Insert into villa values('V14', 'Serene Bliss', '785.95', 'T1'),
('V15', 'Serene no', '585', 'T2'),
('V16', 'Serene yesBliss', '395', 'T3'),
('V17', 'Serene wowBliss', '995', 'T4'),
('V18', 'Serene yayBliss', '700', 'T5'),
('V20', 'Lonelyislan', '200', 'T6');

Insert into Reservation values
('R321', '2020-06-12','C345'),
('R322', '2020-06-13','C745'),
('R323', '2020-06-14','C645'),
('R421', '2020-06-15','C545'),
('R521', '2020-06-16','C445');

Insert into VillaReservation values
('2020-12-01','2020-12-10','V14', 'R321'),
('2020-11-01','2020-11-10','V15', 'R322'),
('2020-10-01','2020-10-10','V16', 'R323'),
('2020-09-01','2020-09-10','V17', 'R421'),
('2020-12-08','2020-08-10','V18', 'R521'),
('2020-12-15','2020-11-10','V18', 'R521');

Query

SELECT v.villaid,
   villaname,
   villacostperday,
   villatypeid
FROM villa v,
     villareservation vr
WHERE v.villaid = vr.villaid
  AND vr.reservationid = NULL;

Answer 1

Use left join with a where condition vr.reservationid is null

SELECT v.villaid,
   villaname,
   villacostperday,
   villatypeid
FROM villa v
LEFT JOIN villareservation vr ON v.villaid = vr.villaid
WHERE vr.reservationid IS NULL

Answer 2

If you want villas that have never booked, NOT EXISTS seems the most direct route:

SELECT v.*
FROM villa v
WHERE NOT EXISTS (SELECT 1
                  FROM villareservation vr
                  WHERE v.villaid = vr.villaid
                 )

;