查询三个表输出什么

Question

我有三个表如下面的截图：

但是，当我想执行下面的查询，我没有得到任何结果，即使是在所有三个表中的数据：

这里是所生成的代码：

SELECT Clients.ClientID, Clients.FirstName, Clients.Surname, Clients.Internal, Clients.Organisation, Clients.LandlineNo, Clients.MobileNo, Clients.Address1, Clients.Town, 
       Clients.Postcode, Clients.Email, Clients.NHS, Clients.PurchaseOrderNumber, Bookings.Date, Bookings.Timebegan, Bookings.Timefinished, Bookings.Price, 
       Bookings.Repeats, Bookings.Rweeks, Bookings.Rdays, Bookings.Rmonths, Bookings.Occurrences, Rooms.Roomname 
FROM  Clients INNER JOIN 
       Bookings ON Clients.ClientID = Bookings.ClientID INNER JOIN 
       Rooms ON Bookings.RoomID = Rooms.RoomID 

Answer 1

Try 

SELECT * 
FROM  Clients LEFT OUTER JOIN 
     Bookings ON Clients.ClientID = Bookings.ClientID 
     LEFT OUTER JOIN Rooms ON Bookings.RoomID = Rooms.RoomID 

请参阅Visual Explanation of SQL Join以更好地理解要使用的内容

如果性能是一个问题，还有其他一些方法。