What are the names of the different customers who have taken out a loan, ordered by the total amount that they have taken?
SELECT T1.cust_name FROM customer AS T1 JOIN loan AS T2 ON T1.cust_id  =  T2.cust_id GROUP BY T1.cust_name ORDER BY sum(T2.amount)
names of different customers who have taken out a loan refers to cust_name from customer table joined with loan table on cust_id; ordered by the total amount they have taken refers to ORDER BY SUM(amount) from loan table;