The analytics team wants to compare the average order value of new and returning customers across sales channels, using data from the orders table.
An order with is_first_order = true is a first order; one with is_first_order = false is a returning order. Orders where is_first_order is NULL belong to neither group, and orders without a recorded amount_usd do not contribute to an average.
Prepare one row per channel with both averages. If a channel has no recorded amounts for one group, its average for that group should be NULL.
Ordering: Sort by channel in ascending order.