CREATE TABLE tags (index NUMBER, id NUMBER, tag CLOB)
CREATE TABLE torrents (groupname CLOB, totalsnatched NUMBER, artist CLOB, groupyear NUMBER, releasetype CLOB, groupid NUMBER, id NUMBER)

What are the artist/groups that released only one CD?
SELECT artist FROM torrents GROUP BY artist HAVING COUNT(*) = 1
SELECT "artist" FROM "torrents" GROUP BY "artist" HAVING COUNT(*) = 1