in Orders added id_client
count_orders do as the interval from 5 to 10 and from 10 to 100000000000000 for example, because otherwise, without functions and additional samples will be problematic
(select count(Orders.id_client) where id_client = ...) BETWEEN Discount.count_orders_min AND Discount.count_orders_max
something like that, not checked for proper operation, but the logic I would think about this
And I would unite the fields, Name Surname , does it make sense to keep them separate?