我收到错误消息：

Object of class mysqli_result could not be converted to string.

代码：

<?php
  $con=mysqli_connect("78.46.51.231","root","","multicraft_daemon");
  if (mysqli_connect_errno($con)){
    echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

  $sql = ("select sum(`memory`) from `server`;");

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

  echo $result;    //$result is mysqli_result and can't be forced to string.
?>

正确的方法是什么？