that are part of order 91245. Each order line refers to an order and to a delivery (if already created). For each order line, up to three time stamps are recorded: the time of entering the order line (column Entered), the time of back ordering (column Back Ordered), and the time of securing the item (column Secured). A null value indicates that the corresponding event did not take place (yet). Typically, only few order lines will be back-ordered (i.e., most rows will have a null value in the Back Ordered column). A backorder is an order line that cannot be delivered because of a lack of sufficient inventory. Therefore, the inventory needs to be replenished before the backorder can be delivered. Since only few order lines become backorders, column Back Ordered has many null values. Once the products are available and reserved for a particular order line, the corresponding timestamp is added in column Secured.