mysql LEFT JOIN主表和两个附加表，每个表的值最大

Question

所以我有三个表：

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

因此，我希望(在单个查询中(为id＝1的用户获得一个单行结果，该结果为：

• 用户表中的所有内容
• 该用户最近条目的黄金值(user_id=1，created_at=MAX(
• Extra表中的最大val4，其中user_id=1

所以结果行看起来像这样：

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

我可以用完成第一部分

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

第二部分是

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

但无论我怎么尝试，我都无法将它们结合在一起。。。我真的很想在单个查询中完成这项工作，显然我可以在多个查询中完成——但我相信这只是我缺乏mysql技能的问题。

谢谢！

Answer 1

只需使用子查询：

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

这是由Users.id:连接的子查询

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

Answer 2

我会使用这样的子查询：

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 ;