mysql查询用于获取在未给出预期结果的日期范围内未预订的所有房间

Question

我正在创建一个预订系统，它有 2 张桌子

房间

id  | name          | no_of_rooms   
1   | Lake View     | 4
2   | Royale        | 2
3   | Sky View      | 6

预订

id |room_id     | start             | end           | total_rooms
4  |1           | 2015-08-13        | 2015-08-14    | 2
5  |2           | 2015-08-20        | 2015-08-22    | 1
6  |2           | 2015-08-01        | 2015-08-13    | 1

在搜索页面上创建新预订时，我想查找此日期范围内的可用房间

搜索值 开始时间：2015-08-11 结束 : 2015-08-12

预期结果

id | name       | no_of_rooms       | available_rooms
1  | Lake View  | 4                 | 4
2  | Royale     | 2                 | 1
3  | Sky View   | 6                 | 6

我得到的结果

id  | name          | no_of_rooms   | available_rooms
1   | Lake View     | 4             | 0
2   | Royale        | 2             | 1
3   | Skyview       | 6             | 0

这是我为房间可用性编写的代码

SELECT 
    r.id, 
    r.name,
    r.no_of_rooms,
    IFNULL(sum(b.total_rooms),0) as available_rooms
FROM rooms r
LEFT JOIN bookings b ON r.id = b.room_id AND 
(
    (b.start <= "2015-08-11" AND b.end >= "2015-08-11")
    OR
    (b.start <= "2015-08-12" AND b.end >= "2015-08-12")
)
GROUP BY r.id

我也不希望显示不可用的房间。无论我尝试什么结果都是完全错误的。希望你们能帮助我！

Answer 1

你可以试试：

SELECT r.id AS roomID, r.name, r.no_of_rooms, 
       r.no_of_rooms - COALESCE(t.bookedRooms,0) AS available_rooms
FROM rooms AS r
LEFT JOIN (
   SELECT room_id, SUM(total_rooms) AS bookedRooms
   FROM bookings
   WHERE `start` < '2015-08-14' AND `end` > '2015-08-11'
   GROUP BY room_id ) AS t
ON r.id = t.room_id
WHERE r.no_of_rooms - COALESCE(t.bookedRooms,0) > 0

查找指定时间段内已预订房间的关键是以下谓词：

`start` <= '2015-08-12' AND `end` >= '2015-08-11'

上面获取所有预订期重叠的房间，即使是一天，与指定的时间段。

在room_id 上使用GROUP BY，我们可以获得指定期间内每个room_id 预订房间的总和。

要获得预期的结果集，我们可以使用派生的预订汇总表执行LEFT JOIN，然后简单地从可用房间数中减去预订房间的总和。

Demo here