How to add Greatest Hits/Compilation Album

I have one MP3 song belonging to, let's say, album1. The same artist of album1 put this song on album2, which is a compilation album of the greatest hits. Anyway, there's one song belonging to many albums, and I don't know how to add this song to the compilation album, without having to get exact same versions of the song with different tags.

Detail: On album1, this song is number 7. On album2, this song is number 2. I also want to tag it with different numbers.

Change the track field.

Try:
ALBUM:
album1\\album2

TRACK:
7\\2

This gives you a multivalue tag fields. But it depends on your mediaplayer if that is diplayer correctly. And for the tracknumber, it's not possible for any mediaplayer to detect what number belongs to what album.

Personally I would keep both files, each for one album.

Didn't work. I'll keep both files then.