I have an important test today on a few basic SQL problem. I studied it in the past but I don't feel 100% confident with these 3 questions:
1 Write a query showing for every author that sold any books how many titles (book_id) and how many units (quantity ordered) they sold;
2 Write a query showing the authors that did not sell any books;
3 Write a query that shows all pairs of customers who bought the same book and the book they bought;
The tables are:
Author (autor_id, book_id) and Customer (customer_id, book_id, quantity_ordered)
Thanks in advance!