mysql - MYSQL 查询：如何用 ORDER BY 合并两个表

Question

谁能帮我解决这个问题？我一直在尝试查询这个，但我不断收到错误。

mysql代码：

SELECT * FROM
(

 SELECT BU.*, BD.BOOK_TITLE AS BOOK_TITLE, BD.BOOK_COMPANY AS COMPANY,
     BD.RETURN_DATE AS RETURN 
 FROM BOOK_USER BU
 INNER JOIN BOOKING_DETAIL BD ON (BU.USR_ID = BD.USR_ID)
                
UNION

 SELECT BU.*, "NEW REGISTERED" AS BOOK TITLE, 'RENT-A-BOOK' AS COMPANY,
     BU.REGISTER_DATE AS RETURN 
 FROM BOOK_USER BU

) AS BU 
GROUP BY BU.USR_ID

表：

BOOK_USER

+---------+----------+---------------+
| USR_ID  | USR_NAME | REGISTER_DATE |
+---------+----------+---------------+
| 1       | john     | 2011-09-20    |
+---------+----------+--------------+
| 2       | jane     | 2011-12-05    |
+---------+----------+--------------+
| 3       | doe      | 2012-02-16    |
+---------+----------+--------------+
| 4       | mary      | 2012-02-02  |
+---------+----------+--------------+

BOOKING_DETAIL

+---------+----------+------------+-----------+--------------+
| BOOK_ID  | USR_ID |  BOOK_TITLE | COMPANY   | RETURN_DATE  |
+----------+--------+-------------+-----------+--------------+
| 1       | 1       | DEAR JOHN   |ABC PVT LMT| 2011-11-01   |
+---------+---------+-------------+-----------+--------------|
| 2       | 1       | LUCKY       |  DEF      | 2012-03-18   |
+---------+---------+-------------+-----------+--------------|
| 3       | 1       | THE RISE    | GHI       | 2012-06-12   |
+---------+---------+-------------+-----------+--------------|
| 4       | 2       | HELLO       |    TIMES  | 2012-01-11   |
+---------+---------+-------------+-----------+--------------|
| 5       | 2       | SHOPAHOLIC  |           | 2012-08-31   |
+---------+---------+-------------+-----------+--------------|
| 6       | 3       | LOST        |           | 2012-06-20   |
+---------+---------+-------------+-----------+--------------|

结果应返回最新的RETURN_DATE 并按 USR_ID 排序。

例如：

1. 约翰，崛起，GHI，2012-06-12
2. 简，购物狂，出租书，2012-08-31
3. 能源部，丢失，租借一本书，2012-06-20
4. 玛丽, 新注册, 出租书, 2012-02-02

Answer 1

该查询包含一个子查询，该子查询为每个用户获取最新信息。 RETURN_DATE

SELECT  a.*, c.BOOK_TITLE, c.RETURN_DATE
FROM    book_user a
        INNER JOIN
        (
            SELECT usr_ID, MAX(return_DATE) maxDate
            FROM booking_detail
            GROUP BY usr_ID
        ) b ON  a.usr_ID = b.usr_ID
        INNER JOIN booking_detail c
            ON  b.usr_ID = c.usr_ID AND
                b.maxDate = c.return_DATE

• SQLFiddle 演示

更新

使用LEFT JOIN和COALESCE

SELECT  a.USR_ID,
        a.USR_NAME, 
        COALESCE(c.BOOK_TITLE,'RENT-A-BOOK') BOOK_TITLE, 
        COALESCE(c.RETURN_DATE, a.REGISTER_DATE) RETURN_DATE
FROM    book_user a
        LEFT JOIN
        (
            SELECT usr_ID, MAX(return_DATE) maxDate
            FROM booking_detail
            GROUP BY usr_ID
        ) b ON  a.usr_ID = b.usr_ID
        LEFT JOIN booking_detail c
            ON  b.usr_ID = c.usr_ID AND
                b.maxDate = c.return_DATE

• SQLFiddle 演示

Answer 2

试试看：

SELECT *
FROM (
    (
        SELECT BU.*, BD.BOOK_TITLE, BD.BOOK_COMPANY AS COMPANY,BD.RETURN_DATE AS RETURN FROM BOOK_USER BU INNER JOIN BOOKING_DETAIL BD ON (BU.USR_ID = BD.USR_ID)
    ) UNION ALL (
        SELECT BU.*, BD.BOOK_TITLE, 'RENT-A-BOOK' AS COMPANY,BD.RETURN_DATE AS RETURN FROM BOOK_USER BU INNER JOIN BOOKING_DETAIL BD ON (BU.USR_ID = BD.USR_ID)
    )
) BU
GROUP BY BU.USR_ID

Answer 3

您可以使用以下查询直接获取输出检查查询：

SELECT BU.*, IFNULL(BD.BOOK_TITLE, 'NEW REGISTERED') AS BOOK_TITLE, IFNULL(BD.BOOK_COMPANY, 'RENT-A-BOOK') AS COMPANY,BD.RETURN_DATE AS RETURN 
FROM BOOK_USER BU
LEFT JOIN (SELECT * FROM (SELECT USR_ID, BOOK_TITLE, BOOK_COMPANY, RETURN_DATE FROM BOOKING_DETAIL ORDER BY RETURN_DATE DESC) AS A GROUP BY USR_ID) AS BD ON (BU.USR_ID = BD.USR_ID) 
ORDER BY BU.USR_ID;