Which musical name has two actors?
select t2.name from actor as t1 join musical as t2 on t1.musical_id = t2.musical_id group by t1.musical_id having count(*) = 2
Show each musical name and the number of actors.
select t2.name, count(*) from actor as t1 join musical as t2 on t1.musical_id = t2.musical_id