>>> orders.head()
        order_date ship_mode customer_id    sales
id
100006  2014-09-07  Standard    DK-13375  377.970
100090  2014-07-08  Standard    EB-13705  699.192
100293  2014-03-14  Standard    NF-18475   91.056
100328  2014-01-28  Standard    JC-15340    3.928
100363  2014-04-08  Standard    JM-15655   21.376