选择城市价格最低的房间

如何解决选择城市价格最低的房间

| 我有3张桌子的房间，酒店，城市，如何选择一个最低价的房间，每个城市的房价为

hotel_id

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,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

但我不确定。     

解决方法

怎么样：

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)

如果没有找到价格更低的房间，这只会从

hotel INNER JOIN room

中选择行。