mysql - 使用 select 子句更新 mysql 作为更新值

Question

我尝试将一个值从 t2.f2 复制到 t1.f1，即 PHPbb3 论坛的主题和帖子表。我尝试过以下sql:

UPDATE t_topics SET
 topic_title = (SELECT t_posts.post_subject WHERE
  t_posts.post_id = t_topics.topic_first_post_id)
WHERE topic_id = 2;

我遇到以下错误:

MySQL said:

`#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE t_posts.post_id = t_topics.topic_first_post_id) WHERE topic_id = 2' at line 1

如何使用 sql 实现此目的？

Answer 1

您缺少 from 子句:

UPDATE t_topics
    SET topic_title = (SELECT t_posts.post_subject
                       FROM t_posts
                       WHERE t_posts.post_id = t_topics.topic_first_post_id
                      )
    WHERE topic_id = 2;