MySQL query with RAND() subquery condition - mysql

Question

I have a nested subquery that selects a random AlbumID that the selected video is in (videos can be in multiple albums), and the outer query then returns the videos and album information based on that AlbumID.
The problem is that the query is returning mixed results; sometimes it gives me some of the videos from one album, sometimes it gives videos from multiple albums, sometimes it returns nothing.
The outer query works if I specify a specific AlbumID instead of the subquery, and the subquery by itself correctly returns 1 random AlbumID. But put together, it's giving me mixed results. What am I missing? Why is it returning varying amounts of rows, and multiple albums?
I've replicated the issue with test data, you can find the CREATE queries here: http://pastebin.com/raw.php?i=e6HaaSGK
The SELECT SQL:
SELECT
Videos_Demo.VideoID,
VideosInAlbums_Demo.AlbumID
FROM
VideosInAlbums_Demo
LEFT JOIN
Videos_Demo
ON Videos_Demo.VideoID = VideosInAlbums_Demo.VideoID
WHERE
VideosInAlbums_Demo.AlbumID = (
SELECT
AlbumID
FROM
VideosInAlbums_Demo
WHERE
VideoID = '1'
ORDER BY
RAND()
LIMIT 1
)

Answer 1

Try this. Moving the subquery to the JOIN seems to fix the problem. I think the problem has to do with having the subquery in the WHERE clause. I think that in the WHERE clause, the subquery and RAND function is being getting executed for each record. This is probably why the results are varying.
SELECT a.AlbumID,
Videos_Demo.VideoID,
VideosInAlbums_Demo.AlbumID
FROM VideosInAlbums_Demo
LEFT JOIN Videos_Demo
ON Videos_Demo.VideoID = VideosInAlbums_Demo.VideoID
JOIN
(
SELECT AlbumID
FROM VideosInAlbums_Demo
WHERE VideoID = '1'
ORDER BY RAND()
LIMIT 1
) AS a ON VideosInAlbums_Demo.AlbumID = a.AlbumID