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

Try this:

In Single Line:

SELECT SUM(Class.Students * Books.Cost) AS BookCost  FROM Books INNER JOIN Class       ON Books.ClassId = Class.ClassId WHERE Books.ClassId =   GROUP BY Books.ClassId

With formatting:

SELECT SUM(Class.Students * Books.Cost) AS BookCost
  FROM Books INNER JOIN Class
   ON Books.ClassId = Class.ClassId
WHERE Books.ClassId = 
GROUP BY Books.ClassId