rental table contains one row for each
rental of each inventory item with information about who
rented what item, when it was rented, and when it was
rental_id: A surrogate primary key that uniquely identifies the rental.
rental_date: The date and time that the item was rented.
inventory_id: The item being rented.
customer_id: The customer renting the item.
return_date: The date and time the item was returned.
staff_id: The staff member who processed the rental.
last_update: When the row was created or most recently updated.