從同一個表中加入具有相同外鍵的 2 個表，但一個表是一對多的

Question

我想查看某個特定會員在我酒店的活動。 我想看看他們去過哪些酒店房間。 但是，如果他們訪問了相同的酒店房間，我只想要該酒店房間的最近一次訪問

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 |
+----------------+-------------+--------+

參與者表的內容基本上是：

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

查找bob活動的預期結果：

+-------------+------------+-----------------+---------------------+-------------------------+
| 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             |
+-------------+------------+-----------------+---------------------+-------------------------+

我不知道如何組合所有者和參與者的driver_id

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

Answer 1

您可以通過首先查找bob所在的每個房間的最大快照日期，然后將其加入快照表以獲取每個房間的最新快照來獲得所需的結果。 然后你需要加入到customers兩次，一次是房間主人的名字，一次是獲取每個參與者的名字：

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, hr.name, c1.driver_id, md.max_date
ORDER BY md.max_date DESC
LIMIT 15

輸出：

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

SQLFiddle 上的演示