Storing an random size array in a mySQL column - php

Question

I have a table. It cointains two columns unique song and genre. Unique song stores a string, doesn't really matter what.
Genres contains an array of strings (genres that apply to the song), number of elements in the strings being random (to big to ditch the array and just make additional columns).
I know that this setup does not work in mySQL as I set it up, but that is what I need.
One way to do it would be serialization, but I would very much like to be able to query out all rock songs without having to first querying them all, unserializing and then finding my match.
Since all of the array contents are of the same type, is there a column that would support such an input? (int is a limited array of ints in a way, no?)

Answer 1

You've got a many-to-many relationship - one song can have multiple genres, and a genre can be used by multiple songs.
Create a table called Song, that contains information about the song and some unique identifier. For the sake of argument, we'll just say it's the name of the song: s_name.
Create a table called Genre, that contains information about genres. Maybe you have the genre, and some information on what style of music it is.
Finally, create a table called SongAndGenre, that'll act as a bridge table. It'll have two column - a song ID (in our case, s_name), and a genre ID (say, g_name). If a song S has multiple genres G1 and G2, you'll have two rows for that song - (S, G1) and (S, G2).

Answer 2

You now have a table, let's say, songs, containing a column genres.
To know the genres of song #123, you can now issue
SELECT genres FROM songs WHERE id = 123;
What you need to do is to create two additional tables:
CREATE TABLE genres (
genre_id integer not null primary key auto_increment,
genre_name varchar(75)
);
CREATE TABLE song_has_genre (
song_id integer not null,
genre_id integer not null
);
To store the fact that song 123 is in genres 'Folk', 'Pop', 'Jazz' and 'Whatever', you can run:
INSERT INTO song_has_genre
SELECT 123, genre_id FROM genres
WHERE genre_name IN ( 'Folk', 'Pop', 'Jazz', ... );
To query what songs are in genre Folk,
SELECT songs.*, genres.genre_name FROM songs
JOIN song_has_genre AS shg ON ( songs.id = shg.song_id )
JOIN genres ON (shg.genre_id = genres.genre_id)
WHERE genres.genre_name = 'Folk';
A bit more work is needed to avoid duplicates if you select two genres and one song is in both, or to retrieve all genres of some songs selected based on genre (i.e., you search 'Pop', and want to find 'Pop,Jazz,Folk', 'Pop,Techno', 'Pop', 'Pop,Whatever', but not 'Techno,Jazz,Folk,Anything except Pop'), but it's doable (e.g. using GROUP_CONCAT and/or GROUP BY, or in the code outside MySQL).