MySQL查詢與左連接和時間條件

Question

我有以下表格：

mysql> select * from room; 
+----+----------+ 
| ID | NAME  | 
+----+----------+ 
| 1 | Room 101 | 
| 2 | Room 102 | 
| 3 | Room 103 | 
+----+----------+ 


mysql> select * from booking; 
+---------+---------------------+---------------------+----------------+ 
| ROOM_ID | START    | END     | GUEST   | 
+---------+---------------------+---------------------+----------------+ 
|  1 | 2016-04-01 00:00:00 | 2016-04-30 00:00:00 | Dorian Gray | 
|  1 | 2016-05-03 00:00:00 | 2016-05-20 00:00:00 | Vanessa Ives | 
|  1 | 2016-05-21 00:00:00 | 2016-05-30 00:00:00 | Ethan Chandler | 
|  2 | 2016-05-06 00:00:00 | 2016-05-18 00:00:00 | John Clare  | 
+---------+---------------------+---------------------+----------------+ 

對於每一個房間，我想獲得有關其預訂狀態的附加信息。如果預訂，我想顯示預訂狀態。如果沒有預訂，則必須顯示NULL。

如果我開始一個基本的查詢..

mysql> select * from room r, booking b where r.id = b.room_id; 
+----+----------+---------+---------------------+---------------------+----------------+ 
| ID | NAME  | ROOM_ID | START    | END     | GUEST   | 
+----+----------+---------+---------------------+---------------------+----------------+ 
| 1 | Room 101 |  1 | 2016-04-01 00:00:00 | 2016-04-30 00:00:00 | Dorian Gray | 
| 1 | Room 101 |  1 | 2016-05-03 00:00:00 | 2016-05-20 00:00:00 | Vanessa Ives | 
| 1 | Room 101 |  1 | 2016-05-21 00:00:00 | 2016-05-30 00:00:00 | Ethan Chandler | 
| 2 | Room 102 |  2 | 2016-05-06 00:00:00 | 2016-05-18 00:00:00 | John Clare  | 
+----+----------+---------+---------------------+---------------------+----------------+ 

它工作正常，但是這不是我想要的..讓我們看看還剩加入...

mysql> select * from room r left join booking b on r.id = b.room_id; 
+----+----------+---------+---------------------+---------------------+----------------+ 
| ID | NAME  | ROOM_ID | START    | END     | GUEST   | 
+----+----------+---------+---------------------+---------------------+----------------+ 
| 1 | Room 101 |  1 | 2016-04-01 00:00:00 | 2016-04-30 00:00:00 | Dorian Gray | 
| 1 | Room 101 |  1 | 2016-05-03 00:00:00 | 2016-05-20 00:00:00 | Vanessa Ives | 
| 1 | Room 101 |  1 | 2016-05-21 00:00:00 | 2016-05-30 00:00:00 | Ethan Chandler | 
| 2 | Room 102 |  2 | 2016-05-06 00:00:00 | 2016-05-18 00:00:00 | John Clare  | 
| 3 | Room 103 | NULL | NULL    | NULL    | NULL   | 
+----+----------+---------+---------------------+---------------------+----------------+ 

儘管如此，顯示重複的......讓我們嘗試與多個條件：

mysql> select * from room r left join booking b on r.id = b.room_id where b.start<now() and b.end>now(); 
+----+----------+---------+---------------------+---------------------+--------------+ 
| ID | NAME  | ROOM_ID | START    | END     | GUEST  | 
+----+----------+---------+---------------------+---------------------+--------------+ 
| 1 | Room 101 |  1 | 2016-05-03 00:00:00 | 2016-05-20 00:00:00 | Vanessa Ives | 
| 2 | Room 102 |  2 | 2016-05-06 00:00:00 | 2016-05-18 00:00:00 | John Clare | 
+----+----------+---------+---------------------+---------------------+--------------+ 

好吧......但是錯了，因爲「103室」不顯示（這不是預訂）.. 。

我希望得到的東西是這樣的：

+----+----------+---------+---------------------+---------------------+--------------+ 
| ID | NAME  | ROOM_ID | START    | END     | GUEST  | 
+----+----------+---------+---------------------+---------------------+--------------+ 
| 1 | Room 101 |  1 | 2016-05-03 00:00:00 | 2016-05-20 00:00:00 | Vanessa Ives | 
| 2 | Room 102 |  2 | 2016-05-06 00:00:00 | 2016-05-18 00:00:00 | John Clare | 
| 3 | Room 103 | NULL | NULL    | NULL    | NULL   | 
+----+----------+---------+---------------------+---------------------+--------------+ 

任何想法？

Answer 1

我不明白爲什麼您使用的是日期時間存儲日期......但無論如何...

SELECT * 
    FROM room r 
    LEFT 
    JOIN booking b 
    ON b.room_id = r.id 
    AND CURDATE() BETWEEN b.start AND b.end; 

Answer 2

下面的查詢應該給你你正在尋找的結果。 SELECT * FROM room r will give you every room number and SELECT * FROM booking b WHERE CURDATE（）BETWEEN b.start AND b.end將爲您提供在START和END日期內包含當天日期的記錄。然後你會LEFT JOIN主查詢與子查詢ON r.id = b.room_id。

SELECT * FROM room r LEFT JOIN 
(SELECT * FROM booking b WHERE CURDATE() BETWEEN b.start AND b.end) b ON r.id = b.room_id;