How to JOIN these 3 tables - php

Question

I have the following JOIN query already done:
$stmt = $cxn->prepare('SELECT p.post_id, p.reply_to, p.parent_id, p.post_path, p.user_id, p.content, p.datetime, p.total_likes, p.total_replies, p.total_reposts, u.username, u.display_name FROM posts p LEFT JOIN users u ON p.user_id = u.user_id WHERE p.user_id IN (SELECT following_id FROM follows WHERE user_id = ?) AND p.removed != 1 ORDER BY p.datetime DESC LIMIT 26');
$stmt->bind_param('i', $user_info[0]);
$stmt->execute();
I have another query that's only purpose is to check if a row exists or not:
$stmt = $cxn->prepare('SELECT COUNT(like_id) FROM likes WHERE post_id = ? AND user_id = ?');
$stmt->bind_param('ii', $row['post_id'], $user_info[0]); // $row['post_id'] is the value of p.post_id from the first query
$stmt->execute();
How would I join the second query into the first one? I've never joined 3 tables so I'm unsure of the procedure.
Thanks.

Answer 1

Joining three tables in a query is like joining two, except... you join three.
Basically it would go something like this:
SELECT p.post_id (...), u.username (...), COUNT(l.like_id) AS nbOfLikes
FROM posts p
LEFT JOIN users u ON p.user_id = u.user_id
LEFT JOIN likes l ON l.post_id = p.post_id AND l.user_id = u.user_id
WHERE p.user_id IN
(SELECT following_id
FROM follows
WHERE user_id = ?)
AND p.removed != 1
ORDER BY p.datetime DESC
LIMIT 26;
-- Actually I think a UNION would perhaps be more adapted to your need concerning the likes table.

Answer 2

If you always have the user_id filled into your table posts and it's a foreign key, avoid to use a left join statement, you can get a better performance using join statement. To join 3 or more tables you can just add the join statement:
SELECT
p.post_id
, p.reply_to
, p.parent_id
, p.post_path
, p.user_id
, p.content
, p.datetime
, p.total_likes
, p.total_replies
, p.total_reposts
, u.username
, u.display_name
FROM posts p
JOIN users u ON p.user_id = u.user_id WHERE p.user_id IN (SELECT following_id FROM follows
JOIN TABLE_2 ON TABLE_2.id = posts.TABLE_id
JOIN TABLE_3 ON TABLE_3.id = posts.TABLE_id
...
WHERE
user_id = ?)
AND p.removed != 1
ORDER BY p.datetime DESC
LIMIT 26