For each language, how many songs are there?
select languages,count(*) from song group by languages
For each language group in order, what is the average duration value of the songs in the group?
select avg(t1.duration) from files as t1 join song as t2 on t1.f_id = t2.f_id group by t2.languages order by t2.languages
How about the maximum duration and resolution?
select max(t1.duration), max(t2.resolution), t2.languages from files as t1 join song as t2 on t1.f_id = t2.f_id group by t2.languages order by t2.languages