What is the average unit price of Rock tracks?
select avg ( t2.unitprice ) from genre as t1 join track as t2 on t1.genreid = t2.genreid where t1.name = "Rock"
What's the average milliseconds of the Rock Tracks?
select avg ( t2.milliseconds ) from genre as t1 join track as t2 on t1.genreid = t2.genreid where t1.name = "Rock"
and for the Jazz tracks?
select avg ( t2.milliseconds ) from genre as t1 join track as t2 on t1.genreid = t2.genreid where t1.name = "Jazz"