Question

I am trying to implement a top-result search for a playlist. The tables are like so:

Playlist: id, title
Assignments: id, youtube_id, position
Videos: youtube_id, title

So joining them is simply: Playlist =(id)= Assignments =(youtube_id)= Videos

I want to find the first playlist on a title match (Titles are not unique) and match it to each of it’s videos, to bring back a list of videos in that playlist. I tried the following query:

SELECT * 
FROM ( 
SELECT id, title, position, youtube_id
FROM playlists p 
JOIN playlist_assignments pa 
USING(id) 
WHERE 1 and title = 'My Top Videos'
LIMIT 1
)d 
JOIN videos v 
USING (youtube_id)
ORDER BY position ASC

Unfortunately, the query will only return 1 row, the playlist matched with just the first video. How can I limit the subquery to just the top result, but still have a final result of a multiple row answer?

Answer 1

The issue with your query is that the sub-query is doing a LIMIT 1, which means that though you retrieved a single playlist but then you also retrieved a single youtube_id. Then when did you ran a JOIN with videos on that single youtube_id, it gives you a single record.

The fix might be to SELECT only from playlists table in the sub-query and move the JOIN for playlist_assignments outside together with the videos join. Something like:

SELECT *
FROM (
    SELECT id, title, position, youtube_id
    FROM playlists p 
    WHERE title = 'My Top Videos'
    LIMIT 1
) d 
JOIN playlist_assignments pa USING (id)
JOIN videos v 
USING (youtube_id)
ORDER BY position ASC;

My suggested query is:

SELECT `p`.`id` `playlist_id`, `p`.`title` `playlist_title`, `v`.`youtube_id` `youtube_id`, `v`.`title` `youtube_title`, `pa`.`position` 
FROM `playlists` `p`
INNER JOIN `playlist_assignments` `pa` ON `p`.`id` = `pa`.`id`
INNER JOIN `videos` `v` ON `pa`.`youtube_id` = `v`.`youtube_id`
WHERE `p`.`title` = 'My Top Videos'
ORDER BY `pa`.`position`;

Hope this helps. Let me know if it worked or if it didn’t.