sql - 如何获取可用座位数

Question

下表是：
Flight (FlightID, MaxCapacity)
FlightBooking (BookingID, FlightID, NumSeats, Status)，状态为：Reserved、Held、Expired、Cancall。

我已经知道如何显示保留和保留席位，但我无法计算应等于 MaxCapacity 减去保留和保留席位的可用席位。

请问有什么建议吗？

Answer 1

SELECT f.MaxCapacity - COUNT(b.Status)
FROM Flight f
INNER JOIN FlightBooking b
ON f.FlightID = b.FlightID
WHERE b.Status IN ('Reserved','Held')
GROUP BY f.FlightID

Answer 2

select flightid, 
       max(f.maxcapacity) - count(case when fb.status in ('reserved', 'held') 
                                       then 1 
                                       else 0 
                                  end)
from flight f
left outer join flightbooking fb on fb.flightid = f.flightid
group by f.flightid