Write a query to return every row in orders with first_amount, the amount of the same customer’s first order, and diff_from_first, the current amount_usd minus that first amount.
Find the first order by order_ts, then order_id, both ascending within each customer. Include every status. The first order’s difference is 0 when its amount is recorded.
Ordering: Sort by customer_id, then order_ts, then order_id, all ascending.