MySQL - 查詢出了什麼問題？

Question

我正在查詢數據庫以查找以下內容。

如果客戶在日期A和B之間搜索城市中的酒店，則在兩個日期之間查找並返回房間空閒的酒店。

每種房型都會有不止一個房間（即5個房間爲A型，10個房間爲B型等），我們必須查詢數據庫才能找到那些至少有一個房間至少有一種房型免費。

這是我的表結構：

**Structure for table 'reservations'** 
    reservation_id 
    hotel_id 
    room_id 
    customer_id 
    payment_id 
    no_of_rooms 
    check_in_date 
    check_out_date 
    reservation_date 

    **Structure for table 'hotels'** 
    hotel_id 
    hotel_name 
    hotel_description 
    hotel_address 
    hotel_location 
    hotel_country 
    hotel_city 
    hotel_type 
    hotel_stars 
    hotel_image 
    hotel_deleted 


    **Structure for table 'rooms'** 
    room_id 
    hotel_id 
    room_name 
    max_persons 
    total_rooms 
    room_price 
    room_image 
    agent_commision 
    room_facilities 
    service_tax 
    vat 
    city_tax 
    room_description 
    room_deleted 

這是我的查詢：

$city_search = '15'; 
$check_in_date = '29-03-2010'; 
$check_out_date = '31-03-2010'; 

$dateFormat_check_in = "DATE_FORMAT('$reservations.check_in_date','%d-%m-%Y')"; 
$dateFormat_check_out = "DATE_FORMAT('$reservations.check_out_date','%d-%m-%Y')"; 

$dateCheck = "$dateFormat_check_in >= '$check_in_date' AND $dateFormat_check_out <= '$check_out_date'"; 

$query = "SELECT $rooms.room_id, 
        $rooms.room_name, 
        $rooms.max_persons, 
        $rooms.room_price, 
        $hotels.hotel_id, 
        $hotels.hotel_name, 
        $hotels.hotel_stars, 
        $hotels.hotel_type 
      FROM $hotels,$rooms,$reservations 
      WHERE $hotels.hotel_city = '$city_search' 
      AND $hotels.hotel_id = $rooms.hotel_id 
      AND $hotels.hotel_deleted = '0' 
      AND $rooms.room_deleted = '0' 
      AND $rooms.total_rooms - (SELECT SUM($reservations.no_of_rooms) as tot 
                FROM $reservations 
                WHERE $dateCheck 
                GROUP BY $reservations.room_id) > '0'"; 

客房每家酒店的每個客房已經預訂的數量將被存儲在保留表。

事情是查詢不會返回任何結果。即使它應該如果我手動計算它。

我試着單獨運行子查詢，我沒有得到任何結果。而且我已經失去了相當數量的頭髮，試圖從昨天開始解決這個查詢。這有什麼問題？還是有更好的方法來做我上面提到的？

編輯：代碼編輯刪除錯誤。感謝Mark Byers。

Sample Data in reservation table 

1 1 1 2 1 3 2010-03-29 2010-03-31 2010-03-17 
2 1 2 3 3 8 2010-03-29 2010-03-31 2010-03-18 
5 1 1 5 5 4 2010-03-29 2010-03-31 2010-03-12 

子查詢應返回

Room ID : 1 Rooms Booked : 7 
Room ID : 2 Rooms Booked : 8 

But it does not return any value at all.... If i remove the dateCheck condition it returns 
Room ID : 2 Rooms Booked : 8 

Answer 1

你的問題是在這裏：

$rooms.total_rooms - (SELECT SUM($reservations.no_of_rooms) as tot, 
               $rooms.room_id as id 
               FROM $reservations,$rooms 
               WHERE $dateCheck 
               GROUP BY $reservations.room_id) > '0'" 

你是做減法total_rooms - (tot, id)其中第一個操作數是標量值，第二個是一張桌子有兩列。刪除結果集中的一列，並確保只返回一行。

您還應該使用JOIN關鍵字進行連接，而不是用逗號分隔表格。這樣你就不會忘記添加連接條件。

你可能想沿着這些路線的東西：

SELECT column1, column2, etc... 
FROM $hotels 
JOIN $rooms 
ON  $hotels.hotel_id = $rooms.hotel_id 
JOIN (
    SELECT SUM($reservations.no_of_rooms) as tot, 
      $rooms.room_id as id 
      FROM $reservations 
      JOIN $rooms 
      ON ??? /* Aren't you missing something here? */ 
      WHERE $dateCheck 
      GROUP BY $reservations.room_id 
) AS T1 
ON  T1.id = room_id 
WHERE $hotels.hotel_city = '$city_search' 
AND $hotels.hotel_deleted = '0' 
AND $rooms.room_deleted = '0' 
AND $rooms.total_rooms - T1.tot > '0'