Complex MySQL query problems and also SQL hangs - mysql

Question

I am trying to write an SQL query which is pretty complex. The requirements are as follows:
I need to return these fields from the query:
track.artist
track.title
track.seconds
track.track_id
track.relative_file
album.image_file
album.album
album.album_id
track.track_number
I can select a random track with the following query:
select
track.artist, track.title, track.seconds, track.track_id,
track.relative_file, album.image_file, album.album,
album.album_id, track.track_number
FROM
track, album
WHERE
album.album_id = track.album_id
ORDER BY RAND() limit 10;
Here is where I am having trouble though. I also have a table called "trackfilters1" thru "trackfilters10" Each row has an auto incrementing ID field. Therefore, row 10 is data for album_id 10. These fields are populated with 1's and 0's. For example, album #10 has 10 tracks, then trackfilters1.flags will contain "1111111111" if all tracks are to be included in the search. If track 10 was to be excluded, then it would contain "1111111110"
My problem is including this clause.
The latest query I have come up with is the following:
select
track.artist, track.title, track.seconds,
track.track_id, track.relative_file, album.image_file,
album.album, album.album_id, track.track_number
FROM
track, album, trackfilters1, trackfilters2
WHERE
album.album_id = track.album_id
AND
( (album.album_id = trackfilters1.id)
OR
(album.album_id=trackfilters2.id) )
AND
( (mid(trackfilters1.flags, track.track_number,1) = 1)
OR
( mid(trackfilters2.flags, track.track_number,1) = 1))
ORDER BY RAND() limit 2;
however this is causing SQL to hang. I'm presuming that I'm doing something wrong. Does anybody know what it is? I would be open to suggestions if there is an easier way to achieve my end result, I am not set on repairing my broken query if there is a better way to accomplish this.
Additionally, in my trials, I have noticed when I had a working query and added say, trackfilters2 to the FROM clause without using it anywhere in the query, it would hang as well. This makes me wonder. Is this correct behavior? I would think adding to the FROM list without making use of the data would just make the server procure more data, I wouldn't have expected it to hang.

Answer 1

There's not enough information here to determine what's causing the performance issue.
But here's a few suggestions and comments.
Ditch the old-school comma syntax for the join operations, and use the JOIN keyword instead. And relocate the join predicates to an ON clause.
And for heaven's sake, format the SQL so that it's decipherable by someone trying to read it.
There's some questions here... will there always be a matching row in both trackfilters1 and trackfilters2 for rows you want to return? Or could a row be missing from trackfilters2, and you still want to return the row if there's a matching row in trackfilters1? (The answer to that question determines whether you'd want to use an outer join vs an inner join to those tables.)
For best performance with large sets, having appropriate indexes defined is going to be critical.
Use EXPLAIN to see the execution plan.
I suggest you try writing your query like this:
SELECT track.artist
, track.title
, track.seconds
, track.track_id
, track.relative_file
, album.image_file
, album.album
, album.album_id
, track.track_number
FROM track
JOIN album
ON album.album_id = track.album_id
LEFT
JOIN trackfilters1
ON trackfilters1.id = album.album_id
LEFT
JOIN trackfilters2
ON trackfilters2.id = album.album_id
WHERE MID(trackfilters1.flags, track.track_number, 1) = '1'
OR MID(trackfilters2.flags, track.track_number, 1) = '1'
ORDER BY RAND()
LIMIT 2
And if you want help with performance, provide the output from EXPLAIN, and what indexes are defined.