How many students live in each city?
select city_code, count(*) from student group by city_code
List the cities from the one with the most students to the one with the least students.
select city_code from student group by city_code order by count(*) desc
How many students live in the most popular city?
select count(*) from student group by city_code order by count(*) desc limit 1
What is the city code of the most popular city?
select city_code from student group by city_code order by count(*) desc limit 1