blog.sql

select
    state,
    sum(total_cost),
    sum(quantity)
from orders
join order_items using (order_id)
join customer using (customer_id) 
group by 1

select 
    state, 
    sum(distinct hash(order_id) + total_cost) - sum(distinct hash(order_id)), 
    sum(quantity) 
from orders 
join order_items using (order_id) 
join customer using (customer_id) 
group by 1

sum(distinct hash(order_id) + total_cost) - sum(distinct hash(order_id))

select 
    state, 
    sum(total_cost), 
    sum(quantity) 
from orders 
join (
    select order_id, sum(quantity) as quantity   
    from order_items
    group by 1
) using (order_id) 
join customers using (customer_id) 
group by 1