SELECT u.username,
      MAX(CASE WHEN b.RowNo=1 THEN b.bookname ELSE NULL END) AS book1,
       MAX(CASE WHEN b.RowNo=2 THEN b.bookname ELSE NULL END) AS book2,
       MAX(CASE WHEN b.RowNo=3 THEN b.bookname ELSE NULL END) AS book3,
       MAX(CASE WHEN b.RowNo=4 THEN b.bookname ELSE NULL END) AS book4
FROM YourUsertable u
INNER JOIN 
(SELECT ROW_NUMBER() OVER(PARTITION BY userid ORDER BY bookid) AS RowNo,*
FROM Yourbooktable) b
ON b.userid=u.userid
GROUP BY u.usernme