Order the artist names by the number of songs.
select t1.artist_name from artist as t1 join song as t2 on t1.artist_name = t2.artist_name group by t2.artist_name order by count(*)
How about the names and the number of songs for the top one artist?
select t1.artist_name, count(*) from artist as t1 join song as t2 on t1.artist_name = t2.artist_name group by t2.artist_name order by count(*) desc limit 1
How about top three?
select t1.artist_name, count(*) from artist as t1 join song as t2 on t1.artist_name = t2.artist_name group by t2.artist_name order by count(*) desc limit 3