Select room with minimal price on city

开发者_JAVA技巧I have 3 table Room, Hotel, City, how can I select one room with minimal price and its hotel_id for each city

price | hotel_id | city_id
10    | 1        | 1
13    | 4        | 2
44    | 7        | 3 
...

SELECT MIN(price) price, hotel_id, city_id FROM (
 SELECT MIN(room_price1) price, hotel_id, city_id 
    FROM Hotel 
    JOIN  Room USING(hotel_id)
        JOIN City USING(city_id)
    LEFT JOIN Service_hotel_option USING (hotel_id)
    WHERE room_price1 > 0
        GROUP BY hotel_id
    ORDER BY price ASC) t 
GROUP BY city_id
ORDER by city_name, price

but I am not sure.

---

How about:

SELECT price, hotel_id, city_id
FROM hotel
INNER JOIN room AS r1 USING (hotel_id)
WHERE NOT EXISTS (SELECT 1 FROM room AS r2
    WHERE r2.hotel_id = r1.hotel_id AND r2.price < r1.price)

This will only select rows from hotel INNER JOIN room if there are no rooms to be found that have lower prices.