How many songs have a resolution below 900?
select count(*) from song where resolution < 900
Among those songs, which ones have mp3 format, show the file size of them.
select t1.file_size from files as t1 join song as t2 on t1.f_id = t2.f_id where t1.formats = "mp3" and t2.resolution < 900
What are the names of songs which have mp3 format and the resolution is below 1000.
select t2.song_name from files as t1 join song as t2 on t1.f_id = t2.f_id where t1.formats = "mp3" intersect select song_name from song where resolution < 1000