ขอคำแนะนำครับ ต้องการสรุปจำนวนนักเรียนใต้รายชื่อสุดท้าย

if($num > 0){
<?php
        $query = "SELECT stu_g.*, stu.student_sex,stu. student_fname, student_lname
        FROM student_group AS stu_g
        INNER JOIN student AS stu ON stu_g.student_username = stu.student_username
        WHERE subject_group_id= '$subject_group_id'  
        ORDER BY student_username ASC  " or die("Error:" . mysqli_error());
        $result = mysqli_query($con, $query); 
              echo ' <table class="table table-hover">';
              echo "<tr>
                     <th>รหัสนิสิต</th>
                     <th>ชื่อ - นามสกุล</th>
                     <th>มา</th>
                     <th>สาย</th>
                     <th>ขาด</th>
                     <th>ลา</th>
              </tr>";
                     while($row = mysqli_fetch_array($result)) {
                            $student_username = $row['student_username'];
                            $student_sex = $row['student_sex'];
                            $student_fname = $row['student_fname'];
                            $student_lname = $row['student_lname'];
                            $check_att = " SELECT attendance_status_id 
                                   FROM check_attendance 
                                   WHERE attendance_id = '$attendance_id' and student_username = '$student_username'"; 
                                   $query_att = mysqli_query($con, $check_att) or die(mysqli_error());
                                   $row_att = mysqli_fetch_array($query_att);
                                        echo "<tr>";
                                        echo "<td>$student_username</td> ";
                                        echo "<td>" .$student_sex .' '.$student_fname .' '.$student_lname."</td> ";
?>
                                        <td><input type='radio' 
                                        <?php if($row_att["attendance_status_id"]=="1")echo" checked";else echo" disabled";?>></td>
                                        <td><input type='radio' 
                                        <?php if($row_att["attendance_status_id"]=="2")echo" checked";else echo" disabled";?>></td>
                                        <td><input type='radio' 
                                        <?php if($row_att["attendance_status_id"]=="3")echo" checked";else echo" disabled";?>></td>
                                        <td><input type='radio' 
                                        <?php if($row_att["attendance_status_id"]=="4")echo" checked";else echo" disabled";?>></td>
                                    <?php
                                        echo "</tr>";
                                    }