PHP SQLite MAX query

$my_conn = new PDO('sqlite:my_student.sqlite3');

<?php 
// Create (connect to) SQLite database in file
$my_conn = new PDO('sqlite:my_student.sqlite3');
// Set errormode to exceptions
$my_conn->setAttribute(PDO::ATTR_ERRMODE, 
                            PDO::ERRMODE_EXCEPTION);
$sql="SELECT max(mark) as m_mark FROM student ";

$result=$my_conn->query($sql);
$row = $result->fetch(PDO::FETCH_OBJ);
echo " Highest Mark : ".$row->m_mark;
?>

Highest Mark : 96

$sql="SELECT * FROM `student` WHERE mark=(select max(mark) from student)";
$result=$my_conn->query($sql);
$row = $result->fetch(PDO::FETCH_OBJ);
echo " Highest Mark : ".$row->mark;
echo " <br>ID  : ".$row->id;
echo " <br>Name  : ".$row->name;
echo " <br>Class  : ".$row->class;
echo " <br>Sex  : ".$row->sex;
?>

Highest Mark : 96
ID : 33
Name : Kenn Rein
Class : Six
Sex : female

$sql="SELECT class,max(mark) as m_mark FROM student group by class";

$step = $my_conn->prepare($sql);
	
$step->execute();
$step = $step->fetchAll();
echo "<table>";
foreach ($step as $row) {
echo "<tr ><td>$row[class]</td><td>$row[m_mark]</td></tr>";
}
echo "</table>";

Eight	79
Five	85
Four	88
Nine	65
Seven	90
Six	96
Three	85