我可以在 MySQL DELETE 语句中使用表别名吗？

Question

这不起作用：

DELETE FROM topics AS t , posts AS p  USING t INNER JOIN p 
WHERE t.id=p.topic_id AND t.id = '5599';

而这样做：

DELETE FROM topics, posts USING topics INNER JOIN posts 
WHERE topics.id=posts.topic_id AND topics.id = '5599';

在 DELETE 语句中使用表别名是无效的还是有其他方法？

我的目标是删除 ID 为 5599 的所有主题和相关帖子posts.topic_id= 5599

Answer 1

我不喜欢USING语法。MySQL 文档显示了以下作为声明要从连接中删除哪些表的方法，这几乎与SELECT语法相同。您当然可以使用别名：

DELETE t, p                  -- delete from both tables 
                             -- this can be used as well:  t.*, p.*
FROM topics AS t 
  JOIN posts AS p
    ON t.id = p.topic_id 
WHERE t.id = 5599 ;

另请注意，id=5599仅当有（至少一个）相关帖子时，这才会删除该主题。如果您无论如何都想删除它（即使没有帖子），请LEFT JOIN改用。

作为记录，您（不工作）的第一条语句在错误的位置对表进行了别名。这应该有效：

DELETE FROM t, p 
USING topics AS t INNER JOIN posts AS p 
WHERE t.id=p.topic_id AND t.id = '5599';

或者更好，使用正确的JOIN语法：

DELETE FROM t, p 
USING topics AS t INNER JOIN posts AS p     -- or: LEFT JOIN
   ON t.id = p.topic_id
WHERE t.id = 5599;