Name of customer whose order is applied with the highest discount.
customer name refers to c_name; the highest discount refers to max(l_discount)
SELECT T3.c_name FROM orders AS T1 INNER JOIN lineitem AS T2 ON T1.o_orderkey = T2.l_orderkey INNER JOIN customer AS T3 ON T1.o_custkey = T3.c_custkey ORDER BY T2.l_discount DESC LIMIT 1