The analytics team wants to understand how a customer's paid-order sizes change after their first paid purchase.
Using orders, assign each paid order an index relative to the first paid order of the same customer, with the first paid order set to 100. For example, an index of 125 means the order amount is 25% higher than that customer's first paid order.
Determine the first paid order using the earliest order_ts. If more than one paid order shares that timestamp, the smaller order_id is the first. Non-paid orders do not determine the reference amount and do not appear in the result.
Round each index to one decimal place.
Ordering: Sort by customer_id, then order_ts, then order_id, all in ascending order.