Which songs have a resolution to be lower than 800?
select song_name from song where resolution < 800
List artist names and the countries of these songs?
select t1.artist_name, t1.country from artist as t1 join song as t2 on t1.artist_name = t2.artist_name where t2.resolution < 800
What about the artist names and countries who have at least one song of resolution above 900?
select t1.artist_name, t1.country from artist as t1 join song as t2 on t1.artist_name = t2.artist_name where t2.resolution > 900 group by t2.artist_name having count(*) >= 1