获取带有喜欢和评论的帖子-一个查询？

Question

I am about to develop a wall for a users-profile. It basically works the same way as Facebooks comment/like system.

So what I want to do is fetch all wall-posts associated with a users profile (by current id variable) and all comments and likes associated with this specific post. I want to use user data from both comments and likes (ie.: name, user_id, email, whatever).

So the question is: Is it possible?

According to this thread's answer it is not: Fetch all news and all comments

According to this thread it is: mysql/php: show posts and for each post all comments

I have tried working with this code but it doesn't seem to work, as it just fetches all comments from DB.

SELECT p.*, c.*, l.*, u.name as post_author, u2.name as comment_author, u3.user_id
FROM edu_wall p
LEFT JOIN edu_comments c ON c.comment_entity = p.post_id
LEFT JOIN edu_likes l ON l.like_entity = p.post_id
LEFT JOIN edu_users u ON u.user_id = p.post_author
LEFT JOIN edu_users u2 ON u2.user_id = c.comment_author
LEFT JOIN edu_users u3 ON u3.user_id = l.like_author

So what is the solution? Should I start up by fetching all wall posts, and then inside that while(), loop comments and likes? It just seems like a very complex and resource-intensive solution.

Thanks in advance!

Answer 1

You can use union for example :

SELECT id, p.name, NULL as "type", u1.username 
FROM edu_wall p 
LEFT JOIN users u1 ON u.id = p.user_id
UNION
SELECT id, NULL as 'name', e.type, u2.username 
FROM edu_likes e 
LEFT JOIN users u2 ON u.id = e.user_id

Null is to replace extra columns between tables, so here when type is NULL then the infos are for edu_wall user and when it's note they are for edu_likes user.

You should try and see youself

Answer 2

This is certainly possible in a single query.

Without knowing your table layouts and what fields you want to use I can't really give any suggested code at the moment.

However the issue is that a single wall post will have numerous comments and numerous likes. You current SQL would bring back one row for every combination of comment and like for each wall post. So if a wall post had 2 comments and 2 likes that would result in 4 rows.

You can get round this a couple of ways. Either make sure you have an order clause on the SELECT and then manually in php process each row and decide if the comment or like is a new one for that wall post. If so process it and if not ignore it.

Alternatively you can use aggregate functions, such as GROUP_CONCAT, to bring back the fields you want in one row. Then explode them out in php. Sql something like this:-

SELECT p.*, u.name as post_author, GROUP_CONCAT(u2.name SEPARATOR '#') as comment_authors, GROUP_CONCAT(u3.user_id SEPARATOR '#') as post_likers
FROM edu_wall p
LEFT JOIN edu_comments c ON c.comment_entity = p.post_id
LEFT JOIN edu_likes l ON l.like_entity = p.post_id
LEFT JOIN edu_users u ON u.user_id = p.post_author
LEFT JOIN edu_users u2 ON u2.user_id = c.comment_author
LEFT JOIN edu_users u3 ON u3.user_id = l.like_author
WHERE p.id = $SomeWallId
GROUP BY p.id