Archive Database Step 7: The Summary Report

Build one report: per country, the number of authors, the number of books, and the average copies held, with countries having no books still shown. Get the joins and the counts right, and report the group sizes rather than only the averages, because an average over one author is not a finding. Then check the totals a second way: the sum of the per-country book counts must equal the total book count. If it does not, a join is dropping or multiplying rows.