Question

我有3个房间，酒店，城市，如何为每个城市选择十个最便宜的房间及其hotel_id 可以为每个城市执行子查询吗？

SELECT price, room_id, hotel_id, city_id
    FROM Hotel 
    JOIN  Room USING(hotel_id)
ORDER BY price
LIMIT 10


Scheme
CREATE TABLE `City` (
  `city_id` int(11) NOT NULL AUTO_INCREMENT,
  `city_name` varchar(50) NOT NULL,
  PRIMARY KEY (`city_id`)
) 

CREATE TABLE `Hotel` (
  `hotel_id` int(11) NOT NULL AUTO_INCREMENT,
  `city_id` int(11) NOT NULL,
  `hotel_name` varchar(100) NOT NULL,
   PRIMARY KEY (`hotel_id`),
   CONSTRAINT `Hotel_FK_1` FOREIGN KEY (`city_id`) REFERENCES `City` (`city_id`) ON DELETE CASCADE ON UPDATE CASCADE
)

CREATE TABLE `Room` (
  `room_id` int(11) NOT NULL AUTO_INCREMENT,
  `hotel_id` int(11) NOT NULL,
  `room_name` varchar(255) DEFAULT NULL,
  `room_price1` int(11) DEFAULT NULL,
  PRIMARY KEY (`room_id`),
  CONSTRAINT `Room_FK_1` FOREIGN KEY (`hotel_id`) REFERENCES `Hotel` (`hotel_id`) ON DELETE CASCADE ON UPDATE CASCADE
)

使用子查询进行查询

SELECT 
     r.room_price1, r.room_id, h.hotel_name, c.city_name
FROM Hotel h 
INNER JOIN Room r ON
    h.hotel_id = r.hotel_id
INNER JOIN City c USING(city_id)
WHERE (
   SELECT count(*) from Room as rt
   JOIN Hotel ht using(hotel_id)
   where c.city_id = ht.city_id and rt.room_price1 < r.room_price1 OR (rt.room_price1 = r.room_price1 AND rt.room_id < r.room_id)
) < 3 
ORDER BY c.city_name, h.hotel_id, r.room_price1

如果一些酒店有一些room_price1这个查询返回超过3行的城市，我需要每个城市3个独特的酒店这个查询可以从一个酒店返回3个房间

生病尝试使用用户代码

set @num := 0, @type := '';
select *
from (
   select r.room_price1 pr, r.room_id, h.hotel_name, c.city_name,
      @num := if(@type = city_id, @num + 1, 1) as row_number,
      @type := city_id as dummy
  from Hotel h
  JOIN Room r USING(hotel_id)
  INNER JOIN City c USING(city_id)
  order by city_name, r.room_price1 asc
) as x where x.row_number <=3;

此方法返回row_number＆lt;的错误排序6（我的初始数据）

Answer 1

有很多关于这个主题的博客文章。

对我来说最有价值的可能是

Xaprb帖子（请参阅“从每个组中选择前N行”一节进行详细说明）

http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/

在你的情况下，这意味着。根据您的需要对此SQL进行建模。

select type, variety, price
from fruits
where (
   select count(*) from fruits as f
   where f.type = fruits.type and f.price < fruits.price
) <= 2;

让我们尝试一下

SELECT 
   r.price, r.room_id, h.hotel_id, h.city_id
FROM Hotel h INNER JOIN Room r ON
  h.hotel_id = r.hotel_id
WHERE (
   select count(*) from Room as rt
   where r.hotel_id = rt.hotel_id and r.price > rt.price
) <= 10;
ORDER BY h.city_id,h.hotel_id,r.price

你可以看到你做了一个子查询来选择所有房间的数量价格低于当前根的价格，看看是否计数小于或等于10.

特别注意我是如何改变

的

f.price < fruits.price

到

r.price > rt.price

因为在Xaprb的例子中他选择了N个最便宜的水果

希望有所帮助。

BTW Stackoverflow不是用于解决作业。你也应该学习一些自己的东西; - ）

Answer 2

我假设表Room引用了它所属的Hotel

SELECT price, room_id, hotel_id, city_id
    FROM Hotel,Room 
    WHERE Hotel.hotel_id = Room.hotel_id
ORDER BY price GROUP BY city_id
LIMIT 10

每个城市十个最便宜的房间

2 个答案: