text: select customer.custkey, customer.name, sum(lineitem.extendedprice * (1 - lineitem.discount)) as revenue, customer.acctbal, nation.name, customer.address, customer.phone, customer.comment
  from customer, orders, lineitem, nation
  where customer.custkey = orders.custkey
  and lineitem.orderkey = orders.orderkey
  and orders.orderdate >= date('1993-10-01')
  and orders.orderdate < date('1994-01-01')
  and lineitem.returnflag = 'R'
  and customer.nationkey = nation.nationkey
  group by customer.custkey, customer.name, customer.acctbal, customer.phone, nation.name, customer.address, customer.comment
  order by revenue asc
  limit 20;