List customers by their most recent order, newest first, and return the first 5.
- •
customer_id - •
last_order_date — the date of their latest order (any status), or NULL if they have never ordered
Customers who never ordered go after everyone who has. Break ties by customer_id ascending. The query must give this order on any engine — don't rely on a default NULL placement (PostgreSQL puts NULLs first under DESC; DuckDB puts them last).