从多个 (4) 表返回记录

Question

我正在尝试编写一个查询，返回多个表中的记录。

ConfRooms 包含房间列表 FIDS_Hardware 包含有关房间中硬件的信息 ConfBookings 包含预订房间列表 ConfRoomOverride 包含有关房间状态的信息，即房间是否设置了覆盖标志

返回“ConfRooms AS c”中的所有记录，其中 c.HotelID = 'EXBHX'。

返回来自“FIDS_Hardware AS h”的所有记录，其中 r.HotelID = 'EXBHX' AND c.ConfRoomID = h.deviceID。

从“ConfBookings AS b”返回所有记录，其中 HotelID = 'EXBHX' AND c.ConfRoomName = b.RoomName。

从“ConfRoomOverride AS o”返回所有记录，其中 HotelID = 'EXBHX' AND c.ConfRoomNID = b.RoomID

目前，我的查询并未返回“ConfRooms”中的所有记录，而是仅返回在 ConfBookings 中具有预订状态的房间。

谁能看到我哪里出错了。

SELECT 
h.messageCount,
h.deviceID, 
c.ConfRoomName, 
r.DisplayMainBoard, 
r.RecordID, 
r.RoomID, 
r.RoomName,
r.RoomBooked,
r.RoomFromDate,
r.RoomToDate,
r.FullBoardRoom, 
COUNT(r.RecordID) AS RC,
r.Override,
r.HotelID,
o.Override AS ConfOverride
FROM
ConfRooms AS c
Left Join FIDS_Hardware AS h ON (c.ConfRoomID = h.deviceID)
Left Join ConfBookings AS r ON (c.ConfRoomName = r.RoomName)
Left Join ConfRoomOverride AS o ON (c.ConfRoomID = o.RoomID)
WHERE c.HotelID = 'EXBHX' 
AND r.HotelID = 'EXBHX'
AND h.hotelID = 'EXBHX'
GROUP BY c.ConfRoomID
ORDER BY h.messageCount DESC,
ConfOverride DESC, 
r.RoomBooked DESC,
c.ConfOrder ASC

Answer 1

试试这个：

SELECT 
h.messageCount,
h.deviceID, 
c.ConfRoomName, 
r.DisplayMainBoard, 
r.RecordID, 
r.RoomID, 
r.RoomName,
r.RoomBooked,
r.RoomFromDate,
r.RoomToDate,
r.FullBoardRoom, 
COUNT(r.RecordID) AS RC,
r.Override,
r.HotelID,
o.Override AS ConfOverride
FROM
ConfRooms AS c
Left Join FIDS_Hardware AS h ON (c.ConfRoomID = h.deviceID AND h.hotelID = 'EXBHX')
Left Join ConfBookings AS r ON (c.ConfRoomName = r.RoomName AND r.HotelID = 'EXBHX')
Left Join ConfRoomOverride AS o ON (c.ConfRoomID = o.RoomID)
WHERE c.HotelID = 'EXBHX' 
GROUP BY c.ConfRoomID
ORDER BY h.messageCount DESC,
ConfOverride DESC, 
r.RoomBooked DESC,
c.ConfOrder ASC

问题是您的 WHERE 子句消除了多个左连接的好处。

当您离开 join FIDS_Hardware AS h 时，这意味着 h 值可以为空，但是当您在 where 子句中执行 "h.hotelID = 'EXBHX'" 时，您只能选择 h 值不为空的行（一行已匹配） .

因此，您需要做的是将这些条件移动到左连接的 ON 子句中，如上所述。