Олег Титаренко

$g=$mysqli->query("SELECT authors.f_name, authors.s_name,books.b_name  FROM authors 
  JOIN author_books ON authors.id=author_books.author_id JOIN 
  books ON books.id=author_books.book_id WHERE authors.f_name='Дмитрий' OR authors.s_name LIKE 'А%' GROUP BY authors.f_name,authors.s_name");

вот так

$g=$mysqli->query("SELECT CONCAT(authors.f_name,' ',authors.s_name) as name, books.b_name  FROM authors 
  JOIN author_books ON authors.id=author_books.author_id JOIN 
  books ON books.id=author_books.book_id WHERE authors.f_name='Дмитрий' OR authors.s_name LIKE 'А%' GROUP BY name");

Выход будет таким

foreach($result as $v){
  echo '<tr>
      <td>'.$v['b_name'].'</td>
      <td>'.$v["name"].'</td>
                            
    </tr> ';
}

SELECT a.*, b.count_book 
FROM authors a, 
        (SELECT author_id, COUNT(book_id) as count_book 
         FROM author_books GROUP BY author_id 
         HAVING COUNT(book_id) > 1) b 
WHERE a.id = b.author_id

ОТВЕТ:
Михаил Шипилов:

$sql = "SELECT a.*, b.count_book FROM authors a,         (SELECT author_id, COUNT(book_id) as count_book          FROM author_books GROUP BY author_id          HAVING COUNT(book_id) > 1) b WHERE a.id = b.author_id";
$results = $mysqli->query($sql); 

foreach($results as $result) {
echo $result['f_name'] . " " . $result['s_name'] . " - " . $result['count_book'] . " книг";
}

Потому что запрос к серверу должен происходить так.
//$_POST[POST_NAME][ROW][NAME];

На выходе должен иметь вид

$_POST[POST_NAME][0][NAME];
$_POST[POST_NAME][1][NAME];
$_POST[POST_NAME][2][NAME];

//Далее расфасовуешь
foreach($_POST[POST_NAME]  as $query) {
if($model->load($query)) {
$model->save();
}
}