房间可用性检查的 SQL 查询

Question

I am trying to create an online room reservation system.

One of the tables of the database is supposed to hold the bookings. It has an autonumber field, customer data fields, two date fields for arrival and departure, and anther table booking details have: bookedid, roomid and room count.

A search page submits the arrival and departure dates to a result page which is then supposed to tell the customer how many rooms are available within the period if any. This is where it all goes wrong. I just can't get an accurate count of the number of rooms already booked within the period requested.

Bookings table

id|guest  | arrive     | depart      
1 |Smith  | 2017-12-20 | 2017-12-25  
2 |Jones  | 2017-12-21 | 2017-12-25  
3 |Brown  | 2017-12-23 | 2017-12-27  
4 |White  | 2017-12-24 | 2017-12-26

Booking Details table

id     | booked_id | room_id |room_count
1      | 1         |  1      | 2
2      | 1         |  2      | 2
3      | 2         |  1      | 4
4      | 3         |  2      | 2
5      | 3         |  1      | 2
6      | 4         |  1      | 2

Rooms table - Room room_id comes from here.

room_id | type        | count   |amount
1       | Single room |  10     | 1000
2       | Deluxe room |  5      | 2000

I want a particular rooms availability (for eg:room_id is 1)

date        available     roomid
2017-12-20  |   8      |  1
2017-12-21  |   4      |  1
2017-12-22  |   4      |  1
2017-12-23  |   2      |  1
2017-12-24  |   0      |  1
2017-12-25  |   0      |  1
2017-12-26  |   4      |  1
2017-12-27  |   8      |  1
2017-12-28  |   10     |  1
2017-12-25  |   10     |  1

I am also using calender table. and i have written a query like

SELECT x.dt , r.room_cnt - COALESCE(SUM(d.`booking_cnt`),0) available
FROM calendar_table x
LEFT JOIN bookings y ON x.dt >= y.`date_from` AND x.dt < y.`date_to`
LEFT JOIN booking_details d ON d.booking_id=y.id
LEFT JOIN rooms r ON r.id= 1
WHERE x.dt BETWEEN now()  AND now() + interval 3 month GROUP BY dt

But this is not working properly.

Answer 1

Modify the query like this,

SELECT x.dt , r.room_cnt,SUM(d.`booking_cnt`) booked,r.room_cnt- SUM(d.`booking_cnt`) available FROM calendar_table x
LEFT JOIN bookings y ON x.dt >= y.`date_from` AND x.dt < y.`date_to`
LEFT JOIN booking_details d ON d.booking_id=y.id and d.room_id='1'
LEFT JOIN rooms r ON r.id= 1
WHERE x.dt BETWEEN now()-interval 3 month AND now() + interval 3 month GROUP BY dt