sql - sql按房间类型计数

Question

我有以下表格结构，我想从预订表中计算所有房间类型。我想要这样的东西： Roomtype :double 3 :simple 5 这有可能吗？

我只计算了预订表中的所有房间

SELECT COUNT(Room_ID)AS NumarRezervari FROM dbo.Reservation WHERE MONTH(Data_Check_in)=5

Answer 1

SELECT Room_Type, COUNT(*) AS NumarRezervari
FROM   dbo.Reservation re
JOIN   dbo.Room ro ON ro.RoomID = re.RoomID
JOIN   dbo.Room_Type rt ON rt.Room_Type_ID = ro.Room_Type_ID
WHERE  MONTH(re.Data_Check_in) = 5
GROUP  BY Room_Type

Answer 2

您需要使用一个GROUP BY子句和几个连接，如下所示：

SELECT Room_Type, count(*) FROM Reservation rv
INNER JOIN Room rm ON rm.Room_ID = rv.Room_ID
INNER JOIN Room_Type rt ON rm.RoomType_ID = rt.RoomType_ID
GROUP BY Room_Type

Answer 3

如果您想计算房间类型的数量，我认为您可以执行以下操作：

select count (Room_Type_Id) from Room_Type
inner join Room on Room.Room_Type_ID = Room_Type.RoomType_ID 
inner join Reservation on Reservation.Room_ID = Room.RoomID 
where ...