Joining multiple Tables and using Count with MySQL - mysql

Question

So I've got myself in a massive confused mess.
Basically, I have a little social network app and I have 4 different tables I need to combine into one view.
Table 1 - User posts
Table 2 - Users
Table 3 - Likes
Table 4 - Comments
I then need to return a list of posts, with the user details and then add columns for the number of likes and number of comments for each post respectively.
If a post doesn't have any likes or comments, then ideally we should show a Zero.
The query below joins everything up, but returns multiple rows of everything, as it is returning 1 row for each comment or like as well.
Anyone able to help me combine these together?
SELECT *
FROM app_posts AS p
LEFT JOIN app_comments AS c ON c.post_id = p.post_id
LEFT JOIN app_user AS u ON u.user_id = p.user_id
LEFT JOIN app_likes AS l ON l.post_id = p.post_id
WHERE u.user_banned = 0
AND p.post_public = 1
ORDER BY p.post_date DESC
Any help would be greatly appreciated!
Table columns are as follows;
app_likes
like_id
post_id
user_id
liked_date
app_comments
comment_id
comment_user_id
post_id
comment_body
comment_date
app_posts
post_id
user_id
post_content
post_date
post_public
app_user
user_id
user_first
user_last
user_avatar
user_banned
An example of what is returned currently is as follows (chopped down for easiness)
You'll see the post_id is repeated multiple times.
What I want it to return is the post_id just once, and with the count of 'likes' and 'comments' in new columns (I don't know how to do this).
Simon

Answer 1

You might be missing GROUP BY...
SELECT p.*,u.*,count(distinct c.comment_id),count(distinct l.like_id)
FROM app_posts AS p
LEFT JOIN app_comments AS c ON c.post_id = p.post_id
LEFT JOIN app_user AS u ON u.user_id = p.user_id
LEFT JOIN app_likes AS l ON l.post_id = p.post_id
WHERE u.user_banned = 0
AND p.post_public = 1
GROUP BY p.post_id
ORDER BY p.post_date DESC
Note that MySQL lets you be sloppy with GROUP BY like this, but a lot of other databases would require you to break out the "p.*" into explicit MAX(p.post_id),MAX(p.post_content), etc.

Answer 2

SELECT p.post_id, COUNT(c.post_id) as num_comments, COUNT(l.like_id) as num_likes
FROM app_posts AS p
LEFT JOIN app_comments AS c ON c.post_id = p.post_id
LEFT JOIN app_user AS u ON u.user_id = p.user_id
LEFT JOIN app_likes AS l ON l.post_id = p.post_id
WHERE u.user_banned = 0
AND p.post_public = 1
GROUP BY p.post_id
ORDER BY p.post_date DESC

Answer 3

Try to add Group by at the end of your query, like this
SELECT *
FROM app_posts AS p
LEFT JOIN app_comments AS c ON c.post_id = p.post_id
LEFT JOIN app_user AS u ON u.user_id = p.user_id
LEFT JOIN app_likes AS l ON l.post_id = p.post_id
WHERE u.user_banned = 0
AND p.post_public = 1
GROUP BY p.post_id
ORDER BY p.post_date DESC