按数据顺序按组更新记录

Question

Theres a note表，每个用户都可以有多个备注。我有一个用户表，其中有一个名为last_note的列null，需要根据notes表中每个用户的最后一个注释进行填充。

为我所做的每个用户选择最新的备注：

SELECT * FROM users
GROUP BY user_id
ORDER BY tm DESC

但是，由于显而易见的原因，我无法将group by和order by子句合并到我的更新查询中：

UPDATE users u
JOIN note n
ON u.id = n.user_id
SET u.last_note = n.note
GROUP BY n.user_id
ORDER BY n.tm DESC

我想知道是否有人可以帮助我弄清楚如何实现这一目标。

提前致谢！

Answer 1

试试这个：

UPDATE users u 
INNER JOIN (SELECT n.user_id, n.note 
            FROM note n 
            INNER JOIN (SELECT n.user_id, MAX(n.noteId) noteId
                        FROM note n GROUP BY n.user_id
                       ) AS A ON n.user_id = A.user_id AND n.noteId = A.noteId
           ) n ON u.id = n.user_id 
SET u.last_note = n.note 

或

UPDATE users u 
INNER JOIN (SELECT n.user_id, n.note 
            FROM (SELECT n.user_id, n.note 
                  FROM note n ORDER BY n.user_id, n.noteId DESC
                 ) n 
            GROUP BY n.user_id
           ) n ON u.id = n.user_id 
SET u.last_note = n.note