(ordr_date, cust_id, product_id, prc_per_unit, unit)
('2020-10-01', '1', 'AA', 10.5, 2),
('2020-11-01', '1', 'BB', 1.5, 3),
('2020-01-01', '1', 'CC', 3.5, 8),
('2020-01-01', '2', 'CC', 4.5, 3),
('2020-01-01', '2', 'BB', 1.5, 3);
1. List the top 20 customers who have the highest spending
2. Find the highest spent product for each customer
