What are the names and ages of every person who is a friend of both Dan and Alice?
select t1.name, t1.age from person as t1 join personfriend as t2 on t1.name = t2.name where t2.friend = 'Dan' intersect select t1.name, t1.age from person as t1 join personfriend as t2 on t1.name = t2.name where t2.friend = 'Alice'