my join returns 0 results - mysql

Question

I have to following 3 tables: room, reservation and reservationroom
Their structure is as follows:
CREATE TABLE `room` (
`roomID` int(11) NOT NULL AUTO_INCREMENT,
`hotelID` int(11) NOT NULL,
`roomtypeID` int(11) NOT NULL,
`roomNumber` int(11) NOT NULL,
`roomName` varchar(255) NOT NULL,
`roomName_en` varchar(255) NOT NULL,
`roomDescription` text,
`roomDescription_en` text,
`roomSorder` int(11) NOT NULL,
`roomVisible` tinyint(4) NOT NULL,
PRIMARY KEY (`roomID`)
) ENGINE=InnoDB AUTO_INCREMENT=29 DEFAULT CHARSET=utf8;
CREATE TABLE `reservation` (
`reservationID` int(11) NOT NULL AUTO_INCREMENT,
`customerID` int(11) NOT NULL,
`hotelID` int(11) NOT NULL,
`reservationCreatedOn` datetime NOT NULL,
`reservationCreatedFromIp` varchar(255) CHARACTER SET greek NOT NULL,
`reservationNumberOfAdults` tinyint(4) NOT NULL,
`reservationNumberOfChildrens` tinyint(4) NOT NULL,
`reservationArrivalDate` date NOT NULL,
`reservationDepartureDate` date NOT NULL,
`reservationCustomerComment` text CHARACTER SET greek,
PRIMARY KEY (`reservationID`)
) ENGINE=InnoDB AUTO_INCREMENT=46 DEFAULT CHARSET=utf8;
CREATE TABLE `reservationroom` (
`reservationroomID` int(11) NOT NULL AUTO_INCREMENT,
`reservationID` int(11) NOT NULL,
`hotelID` int(11) NOT NULL,
`roomID` int(11) NOT NULL,
PRIMARY KEY (`reservationroomID`)
) ENGINE=InnoDB AUTO_INCREMENT=46 DEFAULT CHARSET=utf8;
(please note that foreign keys have been removed from create statements for sake of simplicity)
What I am trying to do: I want to get all rooms that are not reserved for specific dates, that is only the free rooms from the specific hotel (I have its ID)
Here is the query that I have right now:
SELECT r.* FROM room r
LEFT JOIN `reservationroom` rr
ON r.`hotelID` = rr.`hotelID`
AND r.`roomID` = rr.`roomID`
LEFT JOIN `reservation` re
ON rr.`reservationID` = re.`reservationID`
WHERE (rr.`reservationroomID` = ''
OR rr.`reservationroomID` IS NULL
AND re.`reservationArrivalDate` >= 2014-08-27
AND re.`reservationDepartureDate` <= 2014-08-29
AND r.`hotelID` = 10
AND r.`roomVisible` = 1);
This query now returns 0 results. It should return 9 records, since the hotel with ID = 10 has 9 rooms that are free (no resevations for specific dates exist in the reservation table)
Can anyone give me a hand with this please? I am trying to sort this out couple of hours, without any success.

Answer 1

You are using left join, so conditions on all but the first table should be in the on clauses. I think you want a query more like this:
SELECT r.*
FROM room r LEFT JOIN
`reservationroom` rr
ON r.`hotelID` = rr.`hotelID` AND
r.`roomID` = rr.`roomID` LEFT JOIN
`reservation` re
ON rr.`reservationID` = re.`reservationID` AND
re.`reservationArrivalDate` >= 2014-08-27 AND
re.`reservationDepartureDate` <= 2014-08-29
WHERE r.`hotelID` = 10 AND r.`roomVisible` = 1 AND re.reservationID is null;
I'm not sure what the comparison is to the empty string. It doesn't seem necessary for this purpose.