Join and count in DQL

问题:

I have a MySQL command and I cannot find the equivalent in DQL. I am trying to fetch the list most commented posts. Here is the MySQL command :

SELECT posts.id, COUNT(comments.id) AS num
FROM posts
LEFT JOIN comments ON ( posts.id = comments.post_id )
GROUP BY posts.id

Here is the result :

id  num
1   8
2   9
3   17
4   7
5   6
6   20
7   7
8   10
9   14
10  7

In DQL, it should be :

SELECT post, COUNT(comment.id) AS num
FROM Entity\Post post
LEFT JOIN post.comments comment
GROUP BY post.id

But this gives :

id  num
1   50
2   0
3   0
4   0
5   0
6   0
7   0
8   0
9   0
10  0

I don't understand where the 50 comes from and why there is a difference between the 2 results. Could you tell me how to make this join work in Doctrine ?

回答1:

I've made a few test and I found that everything seems to be fine.

Video: id, title, ...
Comment: id, video_id, content, ...

Database schema is very simple and I think there's no need for any explanation.

#DQL:
    SELECT v.id, COUNT(c.id) AS num
    FROM Video v
    JOIN v.comments c
    GROUP BY v.id
    ORDER BY num DESC

#Generated SQL:
    SELECT v0_.id AS id0, COUNT(v1_.id) AS sclr1 
    FROM video v0_ 
    INNER JOIN video_comment v1_ ON v0_.id = v1_.video_id 
    GROUP BY v0_.id 
    ORDER BY sclr1 DESC

#Result set:
    Array
    (
        [0] => Array
            (
                [id] => 148
                [num] => 3
            )

        [1] => Array
            (
                [id] => 96
                [num] => 2
            )

        [2] => Array
            (
                [id] => 111
                [num] => 1
            )

        [3] => Array
            (
                [id] => 139
                [num] => 1
            )

    )

If you select entire Video object instead of its id (v instead of v.id in SELECT clause) the query will execute as well. Of course instead of id element there will be an Video object under 0^th element.

Tested on Doctrine 2.1.0-DEV

回答2:

EDITED: People - This answer does not work. At least you can eliminate this from possible solutions.

SELECT post, COUNT(comment.id) AS num
FROM Entity\Post post
LEFT JOIN post.comments comment
GROUP BY post

You were grouping by post.id, not post

btw, this is a total guess. I don't know DQL, but I do know hibernate, and it seems similar-ish. If it's wrong I'll delete this answer - let me know by comment.

回答3:

I don't know DQL, and this might be stupid....but you posted this:

SELECT post, COUNT(comment.id) AS num
FROM Entity\Post post
LEFT JOIN post.comments comment
GROUP BY post.id

Shouldn't you be selecting post.id? I know it sounds weird, but from what I understand, select post is equivalent to select *. Yet, in your output, you're only getting the ID column. I thought it might be worth noting (even if it isn't).

/prepares for downvote