Query Data from multiple sql tables - mysql

Question

I have an ERD above. I want to get the price of the room based on channel and also the status (isInvisible) of the hotel that owns the room mentioned.
Also a RESTful-API endpoint for that, I tried many times on this assignment and can't get it right as I use Nodejs to write an API GET /api/${roomId}/price but the query doesn't work:
SELECT RoomPrice.price, Status.isInvisible
FROM RoomPrice
INNER JOIN Status
ON (RoomPrice.RoomID = Room.Id AND RoomPrice.ChannelID = ChannelId)
AND (Status.HotelID = Hotels.ID AND Status.ChannelID = ChannelID)
I use query below to create my database in WorkBench:
DROP TABLE IF EXISTS `address`;
CREATE TABLE `address` (
`id` int(9) unsigned NOT NULL AUTO_INCREMENT,
`hotel_id` int(9) unsigned NOT NULL,
`address` varchar(255) NOT NULL,
PRIMARY KEY (`id`),
FOREIGN KEY(hotel_id) REFERENCES hotels(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `address` (`hotel_id`, `address`)
VALUES
(1, '7008 Lynch Centers Apt. 596\nLysannemouth, RI 43355'),
(2, '04795 Stanley Mount Apt. 114\nDorrisborough, DC 38070-3542'),
(1, '24586 Eliseo Haven Suite 045\nKossville, WY 17890-7936'),
(2, '639 Toy Corners\nBashirianfort, CA 08964-7258');
DROP TABLE IF EXISTS `channels`;
CREATE TABLE `channels` (
`id` int(9) unsigned NOT NULL AUTO_INCREMENT,
`url` varchar(255) NOT NULL,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
INSERT INTO `channels` (`id`, `url`, `name`)
VALUES
(1, 'http://www.beahan.com/', 'quod'),
(2, 'http://www.douglas.com/', 'sit');
DROP TABLE IF EXISTS `hotels`;
CREATE TABLE `hotels` (
`id` int(9) unsigned NOT NULL AUTO_INCREMENT,
`name` varchar(100) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;
INSERT INTO `hotels` (`id`, `name`)
VALUES
(1, 'illum'),
(2, 'aliquid');
DROP TABLE IF EXISTS `rooms`;
CREATE TABLE `rooms` (
`id` int(9) unsigned NOT NULL AUTO_INCREMENT,
`hotel_id` int(9) unsigned NOT NULL,
`name` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
FOREIGN KEY(hotel_id) REFERENCES hotels(id)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
INSERT INTO `rooms` (`id`, `hotel_id`, `name`)
VALUES
(1, 1, 'vel'),
(2, 2, 'fugit'),
(3, 1, 'doloribus'),
(4, 2, 'ut'),
(5, 1, 'et');
DROP TABLE IF EXISTS `room_prices`;
CREATE TABLE `room_prices` (
`room_id` int(9) unsigned NOT NULL,
`channel_id` int(9) unsigned NOT NULL,
`price` decimal(10,2) NOT NULL,
PRIMARY KEY (room_id, channel_id),
FOREIGN KEY(room_id) REFERENCES rooms(id),
FOREIGN KEY(channel_id) REFERENCES channels(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `room_prices` (`room_id`, `channel_id`, `price`)
VALUES
(1, 1, '50687.86'),
(1, 2, '6687.86'),
(2, 1, '10687.86'),
(2, 2, '274739.20'),
(3, 1, '3828.63'),
(3, 2, '12525.86'),
(4, 1, '2623587.86'),
(4, 2, '125151.00'),
(5, 1, '2358704.85'),
(5, 2, '7347473.86');
DROP TABLE IF EXISTS `status`;
CREATE TABLE `status` (
`hotel_id` int(9) unsigned NOT NULL,
`channel_id` int(9) unsigned NOT NULL,
`isInvisible` BOOLEAN NOT NULL,
PRIMARY KEY (hotel_id, channel_id),
FOREIGN KEY(hotel_id) REFERENCES hotels(id),
FOREIGN KEY(channel_id) REFERENCES channels(id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `status` (`hotel_id`, `channel_id`, `isInvisible`)
VALUES
(1, 1, false),
(2, 1, true),
(1, 2, true),
(2, 2, true);
I want that once I query to search for the price of roomId (i.e 1) it returns 2 rows (as the mock data only have 2 rows in channels table) that show:
room_id channel_id price isInvisible
1 1 xxxx.xx 0
1 2 xxxx.xx 1
At this moment, I use the query as DRapp help
SELECT
rp.room_id,
rp.channel_id,
rp.price,
s.isInvisible
FROM
room_prices rp
JOIN status s
ON (rp.channel_id = s.channel_id)
JOIN rooms r
ON (rp.room_id = r.id)
JOIN hotels h
ON (r.hotel_id = h.id)
WHERE rp.room_id = 1
It returns 4 rows (instead of 2 rows as expected)
room_id channel_id price isInvisible
1 1 xxxx.xx 0
1 2 xxxx.xx 1
1 1 xxxx.xx 1
1 2 xxxx.xx 1

Answer 1

You need to identify each of the relations as your ERD shows. Each table is joined to its respective context. Dont jump/skip. The only time you can in this scenario is to skip through the channels since the RoomPrice and Status table EACH have a "ChannelId" to qualify the join
SELECT
rp.price,
s.isInvisible
FROM
Room_Prices rp
JOIN Rooms r
on rp.room_id = r.id
JOIN Status s
ON rp.Channel_ID = s.Channel_Id
AND r.hotel_id = s.hotel_id
WHERE
rp.room_id = 1
I had to revise the query. I looked deeper and noticed your CHANNEL table ALSO had the Hotel, so I had to go from the room prices to the room table. From the room table, I can get the hotel. Now that I have the channel from room prices, AND the hotel ID from the rooms table. So NOW I join to the status table on BOTH columns getting the expected single row per room you are expecting.