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

Who or which group is most popular in 2015?
SELECT artist FROM torrents WHERE groupyear = 2015 GROUP BY artist ORDER BY totalsnatched DESC LIMIT 1
SELECT "artist" FROM "torrents" WHERE "groupyear" = 2015 GROUP BY "artist" ORDER BY "totalsnatched" DESC NULLS LAST LIMIT 1