select 
c.cust_name, sum(o2.item_price * o2.quantity ) as total_price 
from 
Customers c 
inner join 
Orders o1
on 
c.cust_id = o1.cust_id 
inner join 
OrderItems o2 
on 
o1.order_num = o2.order_num
group by 
c.cust_name
having
total_price >= 1000
order by 
total_price asc