What are the balances of checking accounts belonging to people with savings balances greater than the average savings balance?
select t2.balance from accounts as t1 join checking as t2 on t1.custid = t2.custid where t1.name in (select t1.name from accounts as t1 join savings as t2 on t1.custid = t2.custid where t2.balance > (select avg(balance) from savings))