Question

我试过这个

select posts.id, posts.title
from posts
inner join (
    select post_id,max(created)
    from comments
    group by post_id
    order by max(created) DESC ) as foo
on posts.id=foo.post_id
order by foo.max(created) DESC;

错误

ERROR 1630 (42000): FUNCTION foo.max does not exist.
Check the 'Function Name Parsing and Resolution' section in the Reference Manual

表

mysql> describe comments;
+----------+--------------+------+-----+---------+----------------+
| Field    | Type         | Null | Key | Default | Extra          |
+----------+--------------+------+-----+---------+----------------+
| id       | int(11)      | NO   | PRI | NULL    | auto_increment |
| post_id  | int(11)      | NO   | MUL | NULL    |                |
| name     | varchar(255) | NO   |     | NULL    |                |
| email    | varchar(255) | NO   |     | NULL    |                |
| body     | varchar(500) | NO   |     | NULL    |                |
| mark     | tinyint(4)   | NO   |     | 1       |                |
| created  | datetime     | YES  |     | NULL    |                |
| modified | datetime     | YES  |     | NULL    |                |
+----------+--------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)



mysql> describe posts;
+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| id          | int(11)      | NO   | PRI | NULL    | auto_increment |
| user_id     | int(11)      | NO   |     | NULL    |                |
| title       | varchar(255) | NO   |     | NULL    |                |
| body        | text         | YES  |     | NULL    |                |
| category_id | int(11)      | NO   |     | NULL    |                |
| tags        | varchar(50)  | NO   |     | NULL    |                |
| mark        | tinyint(4)   | NO   |     | 1       |                |
| created     | datetime     | YES  |     | NULL    |                |
| modified    | datetime     | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)

我需要发布最新评论的帖子。

Answer 1

您在此处使用了错误的引用： -

foo.max(created)

应该是： -

max(foo.created)

错误信息已经显示出问题在哪里，
您应该在遇到错误时始终调试错误消息

但是你没有返回为别名foo创建的列，所以： -

select posts.id, posts.title
from posts
inner join 
(
  select post_id,max(created) AS created
  from comments
  group by post_id 
) as foo
on posts.id=foo.post_id
order by created DESC; <-- you don't need max

Answer 2

没有foo.max功能。

你的意思是：

SELECT posts.id,
       posts.title
FROM   posts
       INNER JOIN (SELECT post_id,
                          created
                   FROM   comments
                   GROUP  BY post_id
                   ORDER  BY Max(created) DESC) AS foo
         ON posts.id = foo.post_id
ORDER  BY Max(foo.created) DESC;

Answer 3

select posts.id, posts.title
from posts
inner join (
    select post_id, max(created) as most_recent
    from comments
    group by post_id) as foo
on posts.id=foo.post_id
order by most_recent DESC;

问题是子查询中的max(created)应该有一个名称。您不需要在子查询中进行排序。

MySql查询错误，可以有人等同查询吗？

3 个答案: