Complicated Query Problem - Booking System

Question

I am currently developing a hotel booking system for my University final year project and am having some serious problems with my queries to calculate room availability.
I felt the best method to calculate room availability was to first calculate which rooms were already booked for any specific queried dates and then to subtract those results from the list of total rooms. That would then return which rooms were available on those dates.
My first query successfully calculated which rooms were already booked using my test dates which were rooms 1,3 & 5. This result was stored in a temporary table. The second query then obtained the list of total rooms (1-10) and from this subtracted the results in the temporary table (1,3 & 5) which should have returned 2,4,6,7,8,9,10 as the rooms available. However, it returned the rather strange result "2,3,4,5,6,7,8,9,10,1,2,4,5,6,7,8,9,10,1,2,3,4,6,7,8,9,10"
It seems to take each result from the temporary table individually, subtract it from the total list of rooms, return the result and then move on to the next value in the temporary table. Which is why '1' is missing from the first 9 numbers, '3' from the second 9 and '5' from the last 9.
If anyone can help me solve this problem or suggest alternative methods I would be most appreciative.
Below is my MySQL code for the relevant parts of my database, the test values I am using and the two queries I am having problems with.
Advance Thanks!
CREATE TABLE booking
booking_id               INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
e_mail                VARCHAR(40),
arrival_date          DATE NOT NULL,
departure_date          DATE NOT NULL,
PRIMARY KEY(booking_id)
insert into booking (booking_id,e_mail,arrival_date,departure_date)
values ('[email protected]','2004-02-25','2004-02-28');
CREATE TABLE roombooked
booking_id      INTEGER UNSIGNED NOT NULL REFERENCES booking(booking_id),
room_id               INTEGER UNSIGNED NOT NULL REFERENCES rooms(room_no),
no_of_nights          INTEGER UNSIGNED NOT NULL,
PRIMARY KEY(booking_id,room_id)
insert into roombooked(booking_id,room_id,no_of_nights)
values ('1','1','1'),('1','3','1'),('1','5','1');
CREATE TABLE rooms
room_no               INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,
room_name           VARCHAR(11),
room_type               VARCHAR(9),
single_price          DECIMAL(5,2),
double_price          DECIMAL(5,2),
PRIMARY KEY(room_no)
insert into rooms (room_name,room_type,single_price,double_price)
values ('shakespeare','principal','165','225'),
('keats','principal','165','225'),
('kipling','standard','125','165'),
('tennyson','superior','135','185'),
('shelley','deluxe','155','205'),
('brooke','superior','135','185'),
('wordsworth','deluxe','155','205'),
('milton','deluxe','155','205'),
('masefield','deluxe','155','205'),
('browning','deluxe','155','205');
FIRST QUERY
CREATE TEMPORARY TABLE roomsoccupied          
SELECT roombooked.room_id FROM roombooked, booking
WHERE
roombooked.booking_id = booking.booking_id
AND
booking.arrival_date = '2004-02-25'
AND
booking.departure_date = '2004-02-28';
SECOND QUERY
SELECT rooms.room_no FROM rooms, roomsoccupied
WHERE
rooms.room_no != roomsoccupied.room_id;

Answer 1

you haven't got a join in your second query
SECOND QUERY
SELECT rooms.room_no FROM rooms, roomsoccupied
WHERE
rooms.room_no != roomsoccupied.room_id;will return rubbish because you have created a valid view of your data with a sensible join.
try something like
SELECT rooms.room_no FROM rooms
WHERE rooms.room_no NOT IN (SELECT roomsoccupied.room_id FROM roomsoccupied);instead, which I believe should give you more meaningful data