@H_301_1@$q = $this->db->select(' books.title,reserved_books.id,reserved_books.isbn,reserved_books.price,reserved_books.item_sold,reserved_books.date_sold,reserved_books.total_amount ') ->from('reserved_books') ->join('books','reserved_books.isbn= books.isbn') ->limit($limit,$offset);

我怎么能在我的查询中使用distinct？
reserved_books.isbn是唯一的.