Mini Shell

<?php 
    include '../db/database.php';
    
    $year = $_POST['year'];
    $user_id = $_POST['user_id'];
    $username = $_POST['username'];
    $sex = $_POST['sex'];
    $password = $_POST['username'];
    $name_peple = $_POST['name_peple'];
    $sname_peple = $_POST['sname_peple'];
    $user_class_id = $_POST['user_class_id'];
    
    $sql_student = "SELECT username FROM users_dg WHERE username='$username' AND year='$year' AND user_class_id='$user_class_id' AND name_peple='$name_peple' AND sname_peple='$sname_peple' AND sex='$sex' ";
    $result_student = mysqli_query($link2, $sql_student);
    $is_student = mysqli_num_rows($result_student);
    if ($is_student == 1) {
        header('Content-Type: application/json');
        $errors = "รหัสและห้องเรียนมีอยู่แล้วในระบบ" . mysqli_error($link2);
        echo json_encode(array('status' => 'danger','message' => $errors));
        exit;
    }
    
     $sql = "UPDATE `users_dg` SET `year`='$year',`username`='$username',`sex`='$sex',`password`='$password',`name_peple`='$name_peple',`sname_peple`='$sname_peple',`user_class_id`='$user_class_id'  WHERE (`user_id`='$user_id')";
     $result = mysqli_query($link2, $sql);
     
   if ($result) {
         header('Content-Type: application/json');
         echo json_encode(array('status' => 'success','message' => 'แก้ไขข้อมูลเรียบร้อยแล้ว'));     
    } else {
        header('Content-Type: application/json');
        $errors = "เกิดข้อผิดผลาดไม่สามารถบันทึกข้อมูลได้" . mysqli_error($link);
        echo json_encode(array('status' => 'danger','message' => $errors));
    }