title: Trying to use a subquery to find two things from two different tables
body: <p>I want to find the book code and book title for each book found in branch number 2 and written by author 20. </p>
  
  <p>the book code and title are found in the "book" table
  branch number is found in the 'branch' table 
  the "author" table has the author number
  theres also a table called 'inventory' that has book code and branch number</p>
  
  <p>any help would be greatful!</p>
  
  <p>This is what I tried:
  SELECT BOOK_CODE, TITLE
  FROM BOOK
  WHERE BOOK_CODE IN
      (SELECT BOOK_CODE
      FROM INVENTORY
      WHERE BRANCH_NUM = '2'
      AND AUTHOR_NUM = '20');</p>