iTunes albums with more than one artist singing

I have many albums that feature duets, main artist and guest. In iTunes the album shows up once for each duet (with the one song featuring the duet) and then the main album featuring just the main artist. How can I combine these, without creating a playlist for each album? Thanks.

Hit Cmd+I on the two files, then change the "album artist" column to the main artists album. this will then combine the two under the album artists name. You can leave the "artist" column as "singer+guest".