使用php和mysql更新某些用户

输入他们的个人资料后，我正在尝试更新一些用户。

这是将我转移到他们的个人资料页面的按钮。一切正常，直到我尝试更新一些信息。

这是个人资料页面：

  $db = mysqli_connect('localhost', '###', '###', '###');
  $sql = "SELECT * FROM clients  WHERE id='".$id."'  ";

  $result = mysqli_query($db, $sql);

    $resultCheck = mysqli_num_rows($result);

    if ($resultCheck > 0) {

    echo "<table>
            <tr>
                <th> Naam </th>
                <th> id </th>
                <th> email </th>

            </tr>";
        while ($row = mysqli_fetch_assoc($result)) {
      echo "<tr>";
            echo  "<td>" . $row['name'] . "</td>";
            echo  "<td>" . $row['id'] . "</td>";
            echo "<td>" . $row['email']  . "</td>";   

            $name = $row['name'];
            $email = $row['email'];

    }
  }  

    if (isset($_POST['pinfo'])) {

      $query = "UPDATE clients SET name=? , email=?
       WHERE id=?";
      $stmt = mysqli_prepare($db, $query);
      mysqli_stmt_bind_param($stmt, 'sss',   $_POST['name'], $_POST['email'], $id);
      mysqli_stmt_execute($stmt);
   }

尝试更新后，我仅收到错误消息“ Undefined index：id”