What are the names of all movies?
select title from movie
How many ratings did each of them have?
select count(*) from rating as t1 join movie as t2 on t1.mid = t2.mid group by t1.mid
Give me the name of the movie that has the most ratings.
select t2.title, t1.mid from rating as t1 join movie as t2 on t1.mid = t2.mid group by t1.mid order by count(*) desc limit 1