[sql] "You tried to execute a query that does not include the specified aggregate function"

SELECT SUM(orders.quantity) AS num, fName, surname
FROM author
INNER JOIN book ON author.aID = book.authorID;

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?

I had a similar problem in a MS-Access query, and I solved it by changing my equivalent fName to an "Expression" (as opposed to "Group By" or "Sum"). So long as all of my fields were "Expression", the Access query builder did not require any Group By clause at the end.

GROUP BY can be selected from Total row in query design view in MS Access.
If Total row not shown in design view (as in my case). You can go to SQL View and add GROUP By fname etc. Then Total row will automatically show in design view.
You have to select as Expression in this row for calculated fields.