How many schools have a school bus?
select count(*) from school_bus as t1 join school as t2 on t1.school_id = t2.school_id
How many school buses does each school type have?
select count(*) from school_bus as t1 join school as t2 on t1.school_id = t2.school_id group by t2.type
Please also show the types.
select t2.type, count(*) from school_bus as t1 join school as t2 on t1.school_id = t2.school_id group by t2.type