MySQL Query for book cost of a class

Question

I just need a single MySQL line query for the following.

Lets say there are 2 simple tables: Class and Books<

Answer 1

Did you mean something like:

SELECT C.Name AS ClassName, SUM(B.Price) * C.Students AS BookCost
  FROM Class AS C INNER JOIN
       Books AS B ON C.ID = B.ClassId
  WHERE C.ID IN (SELECT ID
                   FROM Class
                   WHERE Students >= 31
                   ORDER BY Students ASC
                   LIMIT 1)
  GROUP BY C.ID;