mysqli - How to use SQL statement given below in codeigniter? -

how use sql given below in codeigniter?

select *   borrow_book  isbn=(select isbn             add_book              author='$author) 

use this

$query= $this->db->query("select borrow_book.*                              borrow_book, add_book                             borrow_book.isbn= add_book.isbn , add_book.author = '$author'"); $result= $query->result_array(); return $result;