title: "You tried to execute a query that does not include the specified aggregate function"
body: <pre><code>SELECT SUM(orders.quantity) AS num, fName, surname
  FROM author
  INNER JOIN book ON author.aID = book.authorID;
  </code></pre>
  
  <p>I keep getting the error message: "you tried to execute a query that does not include the specified expression "fName" as part of an aggregate function. What do I do?</p>