ferent ways: by
                            product SKU and by product name.
                    </p>
      <p>
                        In our data set, the product SKU is required to be
                        unique, so we use that as the primary key. The
                        product name, however, is not a unique value so we
                        set this up as a secondary key.
                    </p>
      <p>
                         The class appears as follows in our example:
                  