mysql LEFT JOIN主表和另外兩個表，每個表都有最大值

Question

所以我有三個表：

Users
+-------+-----+----+
| id    | val1|val2|
+-------+-----+----+
| 1     |  1  |3   |
| 2     |  2  |5   |
| 3     |  4  |7   |
+-------+-----+----+

UsersData
+----+--------------+------------+-----|
| id | users_id     | created_at | gold|
+----+--------------+------------+-----|
|  9 |  1           |121454561212| 14  |
|  10|  1           |131454561212|  2  |
|  11|  2           |111454561212| 99  |
+----+--------------+------------+-----+

Extra
+----+------------+-----|
| id | users_id   | val4|
+----+------------+-----|
|  1 |  1         |  5  |
|  2 |  1         |  6  |
|  3 |  1         |  7  |
+----+------------+-----+

所以我希望實現（在單個查詢中）是為id = 1的用戶獲取單行結果，該結果滿足：

• 用戶表中的所有內容
• 該用戶的最新條目的黃金值（users_id = 1，created_at = MAX）
• Extra表中最大的val4，其中users_id = 1

因此結果行將如下所示：

+-------+-----+----+-----+----+
| id    | val1|val2|gold |val4|
+-------+-----+----+-----+----|
| 1     |  1  |3   | 2   |  7 |
------------------------------+

我可以完成第一部分

SELECT Users.id, Users.val1, Users.val2, UsersData.gold
FROM UsersData
LEFT JOIN Users ON UsersData.users_id = Users.id
WHERE Users.id = 1 
ORDER BY UsersData.created_at DESC
LIMIT 1

第二部分

SELECT MAX(Distances.distance) AS maxdistance FROM Distances WHERE Distances.users_id = 1

但是無論如何嘗試，我都無法將它們組合在一起……我真的很想在單個查詢中完成此任務，顯然我可以使用多個查詢來完成-但我認為這只是我缺乏mysql技能而已這里。

謝謝！

Answer 1

只需使用子查詢：

SELECT Users.id, Users.val1, Users.val2, UsersData.gold,
(SELECT MAX(Distances.distance) FROM Distances WHERE Distances.users_id = Users.id) AS maxdistance
FROM UsersData
RIGHT JOIN Users ON UsersData.users_id = Users.id
WHERE Users.id = 1 
ORDER BY UsersData.created_at DESC
LIMIT 1

這是由Users.id連接的子查詢：

SELECT MAX(Distances.distance) FROM Distances WHERE Distances.users_id = Users.id) AS maxdistance

Answer 2

我將使用以下子查詢：

select u.*,
       (select ud.gold
        from userdata ud
        where ud.users_id = u.id
        order by ud.created_at desc
        limit 1
       ) as most_recent_gold,
       (select max(e.val4)
        from extra e
        where e.users_id = u.id
       ) as max_val4
from users u
where u.id = 1 ;