CREATE TABLE loan (cust_id VARCHAR, amount INT)
CREATE TABLE customer (cust_name VARCHAR, cust_id VARCHAR)

List the name of all different customers who have some loan sorted by their total loan amount.
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)
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") NULLS FIRST