What is the name of the user that has the lowest checking balance?
select t1.name from accounts as t1 join checking as t2 on t1.custid = t2.custid order by t2.balance limit 1
the lowest saving balance?
select t1.name from accounts as t1 join savings as t2 on t1.custid = t2.custid order by t2.balance limit 1
how about the lowest total sum of checking and saving balance?
select t1.name 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 + t3.balance limit 1