Averages are skewed by one huge order. The median is more robust, but SQLite (like many databases) has no MEDIAN function.
Return a single row with one column, median_order_value: the median of all order totals. With an even number of orders, it's the average of the two middle values.
Schema
customers(id, name, country, signup_date)
orders(id, customer_id, order_date, total)