连接来自同一表的具有相同外键但两个表一对一的表

如何解决连接来自同一表的具有相同外键但两个表一对一的表

我想查看我酒店中特定成员的活动。我想看看他们去过哪些酒店房间。但是，如果他们访问了相同的酒店房间，我只希望最近一次访问该酒店房间

customers
+--------+-------+-----------+
| cus_id | name  | driver_id |
+--------+-------+-----------+
|      1 | bob   |     11111 |
|      2 | james |     22222 |
|      3 | sam   |     33333 |
|      4 | billy |     44444 |
+--------+-------+-----------+


hotel_rooms (cus_id is the owner of the room)
+----------+------------+--------+
| hroom_id |    name    | cus_id |
+----------+------------+--------+
|        1 | small room |      3 |
|        2 | big room   |      1 |
+----------+------------+--------+

snapshots (when we detected the user in the room)
+-------------+----------+---------------------+
| snapshot_id | hroom_id |     date_added      |
+-------------+----------+---------------------+
|           1 |        1 | 2020-01-12 12:43:13 |
|           2 |        1 | 2020-01-13 17:23:53 |
|           3 |        2 | 2020-01-19 07:34:01 |
+-------------+----------+---------------------+

participants (who was also present in the same room at the particular time we detected the customer in the room)
+----------------+-------------+--------+
| participant_id | snapshot_id | cus_id |
+----------------+-------------+--------+
|              1 |           1 |      1 |
|              2 |           1 |      3 |
|              3 |           2 |      1 |
|              4 |           2 |      2 |
|              5 |           2 |      3 |
|              6 |           3 |      1 |
|              7 |           3 |      4 |
+----------------+-------------+--------+

从本质上说，参与者表是：

• snapshot_id=1 bob和sam在small room中。
• snapshot_id=2，bob，james和sam在small room中。
• snapshot_id=3，bob和billy在big room中。

查找bob活动的理想结果：

+-------------+------------+-----------------+---------------------+-------------------------+
| snapshot_id |    name    | owner_driver_id |     date_added      | participants_driver_ids |
+-------------+------------+-----------------+---------------------+-------------------------+
|           2 | small room |           33333 | 2020-01-13 17:23:53 | 11111,22222,33333       |
|           3 | big room   |           11111 | 2020-01-19 07:34:01 | 11111,44444             |
+-------------+------------+-----------------+---------------------+-------------------------+

我不知道如何将所有者和参与者的driver_id组合在一起

SELECT s.snapshot_id,hr.name,c.driver_id as owner_driver_id,MAX(s.date_added) as date_added,GROUP_CONCAT(p.driver_id) as participants_driver_ids
FROM hotel_rooms hr INNER JOIN
snapshots s
ON hr.hroom_id = s.hroom_id JOIN
participants p
ON s.snapshot_id = p.snapshot_id JOIN
customers c
ON hr.cus_id = c.cus_id
WHERE p.cus_id = 1
GROUP BY hr.cus_id
ORDER BY date_added

解决方法

首先要找到bob所在的每个房间的最大快照日期，然后将其加入快照表以获取每个房间的最新快照，以获得所需的结果。然后，您需要两次加入customers，一次是会议室所有者的名字，一次是获得每个参与者的名字：

SELECT s.snapshot_id,hr.name,c1.driver_id AS owner_driver_id,md.max_date AS date_added,GROUP_CONCAT(c2.driver_id) AS participants_driver_ids 
FROM snapshots s
JOIN (
  SELECT hr.hroom_id,MAX(date_added) AS max_date
  FROM hotel_rooms hr
  JOIN snapshots s ON s.hroom_id = hr.hroom_id
  JOIN participants p ON p.snapshot_id = s.snapshot_id
  JOIN customers c ON c.cus_id = p.cus_id
  WHERE c.name = 'bob'
  GROUP BY hr.hroom_id,hr.name
) md ON md.hroom_id = s.hroom_id AND md.max_date = s.date_added
JOIN hotel_rooms hr ON hr.hroom_id = s.hroom_id
JOIN customers c1 ON c1.cus_id = hr.cus_id
JOIN participants p ON p.snapshot_id = s.snapshot_id
JOIN customers c2 ON c2.cus_id = p.cus_id
GROUP BY s.snapshot_id,c1.driver_id,md.max_date
ORDER BY md.max_date DESC
LIMIT 15

输出：

snapshot_id     name        owner_driver_id     date_added              participants_driver_ids
2               small room  33333               2020-01-13 17:23:53     11111,33333,22222
3               big room    11111               2020-01-19 07:34:01     44444,11111

Demo on SQLFiddle