How many schools are there?
select count(*) from school;
Show me their locations.
select location from school;
Which of them have more than 3 players?
select t2.location from player as t1 join school as t2 on t1.school_id = t2.school_id group by t1.school_id having count(*) > 3;
How about more than 1 player?
select t2.location from player as t1 join school as t2 on t1.school_id = t2.school_id group by t1.school_id having count(*) > 1;