Question

Been stuck with this fairly simple MySQL query for a day now! Can’t believe how quickly I’ve forgotten the basics. I have 3 tables – user, post and favourite_post. The post table has a user_id that is a FK to user table.

The favourite_post table has

user_id REFERENCES user(id) 
post_id REFERENCES post(id)
timestamp 

When a user favourites a post, his user_id, the post_id and timestamp are inserted into the favourite_post table.

I use the following query to retrieve the 15 more recent posts

SELECT post.id, post.text, post.timestamp, post.user_id, user.username 
FROM post 
   INNER JOIN user 
   ON post.user_id = user.id 
ORDER BY post.id 
DESC LIMIT 15;

What I need to do along with that is check if each post has been favourited by the current user(say user_id = 1) by joining with the favourite_post table.

Answer 1

    SELECT p.id, p.text, p.timestamp, p.user_id, u.username, 
           IF(ISNULL(fp.post_id), 'No', 'Yes') has_favourite
      FROM post p
INNER JOIN user u
        ON p.user_id = u.id 
 LEFT JOIN favourite_post fp
        ON p.id = fp.post_id
       AND u.id = fp.user_id
  ORDER BY p.id DESC 
     LIMIT 15;