Question

交

+-----+-----+-----+
| tid | uid | pid |
+-----+-----+-----+
|   1 |   1 |   1 |
|   2 |   1 |   2 |
|   3 |   1 |   3 |
|   3 |   2 |   4 |
|   4 |   1 |   5 |
...
+-----+-----+-----+

螺纹

+-----+---------+---------+
| tid | lastpid | lastuid |
+-----+---------+---------+
|   1 |       0 |       0 |
|   2 |       0 |       0 |
|   3 |       0 |       0 |
|   4 |       0 |       0 |
...
+-----+---------+---------+

我希望线程的结果是：

+-----+---------+---------+
| tid | lastpid | lastuid |
+-----+---------+---------+
|   1 |       1 |       1 |
|   2 |       1 |       2 |
|   3 |       2 |       4 |
...
+-----+---------+---------+

你如何用一个陈述完成它？帖子的tid = thead的tid，并发布max（pid）的pid，uid是thead的值。

我想从post.tid eq thread.tid的post max（pid）获得pid和uid。并设置pid，uid来替换thread的lastpid和lastuid。

根据最佳答案，我们重写了它来解决这个问题： UPDATE thread t INNER JOIN ( SELECT tid, uid AS last_uid, pid AS last_pid FROM post WHERE pid IN (SELECT max(pid) FROM post GROUP BY tid) ) p ON t.tid = p.tid SET t.lastuid = p.last_uid, t.lastpid = p.last_pid;

Answer 1

您可以尝试更新加入：

UPDATE thread t
INNER JOIN
(
    SELECT tid, MAX(uid) AS max_uid, MAX(pid) AS max_pid
    FROM post
    GROUP BY tid
) p
    ON t.tid = p.tid
SET
    t.lastuid = p.max_pid,
    t.lastpid = p.max_uid;

如果您只想进行选择，则可以稍微修改上述内容，基本上只需将UPDATE...替换为SELECT即可。

请注意，lastuid和lastpid似乎已在您的预期输出中进行了交换。

mysql从另一个表更新列值

1 个答案: