how many artists do you have?
select count ( distinct artistid ) from artist
What are their names?
select name from artist
how many albums does AC/DC have?
select count ( * ) from album as t1 join artist as t2 on t1.artistid = t2.artistid where t2.name = "AC/DC"
And for Metallica?
select count ( * ) from album as t1 join artist as t2 on t1.artistid = t2.artistid where t2.name = "Metallica"