What is the savings balance of the account belonging to the customer with the highest checking balance?
SELECT T3.balance FROM accounts AS T1 JOIN checking AS T2 ON T1.custid  =  T2.custid JOIN savings AS T3 ON T1.custid  =  T3.custid ORDER BY T2.balance DESC LIMIT 1
savings balance = T3.balance; highest checking balance refers to MAX(T2.balance); account belonging to the customer = JOIN on custid;