inventory table contains one row for
each copy of a given film in a given store.
inventory table refers to the
tables using foreign keys and is referred to by the
inventory_id: A surrogate primary key used to uniquely identify each item in inventory.
film_id: A foreign key pointing to the film this item represents.
store_id: A foreign key pointing to the store stocking this item.
last_update: When the row was created or most recently updated.