Please find the below correction in the book under the Grouping section In the book: --in SQL %sql SELECT count(*) FROM dfTable GROUP BY InvoiceNo, CustomerId +---------+----------+-----+ |InvoiceNo|CustomerId|count| +---------+----------+-----+ | 536846| 14573| 76| | 537026| 12395| 12| | 537883| 14437| 5| ... | 543188| 12567| 63| | 543590| 17377| 19| | C543757| 13115| 1| | C544318| 12989| 1| +---------+----------+-----+ correct one: --in SQL Select InvoiceNo, CustomerId, count(*) from dfTable Group by InvoiceNo, CustomerId could you please modify the source accordingly?