what are the names of all dorms?
select dorm_name from dorm
how many students are living in each dorm? Group by names of dorms.
select count(*), t3.dorm_name from student as t1 join lives_in as t2 on t1.stuid = t2.stuid join dorm as t3 on t3.dormid = t2.dormid group by t3.dorm_name
how many students are older than 20 years old in each dorm?
select count(*), t3.dorm_name from student as t1 join lives_in as t2 on t1.stuid = t2.stuid join dorm as t3 on t3.dormid = t2.dormid where t1.age > 20 group by t3.dorm_name