Archive Database Step 5: Join and Verify

Write a query listing every book with its author and that author's country. Then verify it properly: count the rows in books alone, count the rows in your joined result, and explain any difference. If they match, deliberately add a book with a NULL author_id and run it again, so you have watched a row disappear. Then write down, in one sentence, the question your join actually answers, because it is not always the one you set out to ask.