order by / group by

Ja, jeg skal have stillet nogle tal op efter hinanden i en tabel, jeg har brugt SUM() til at lægge nogle tal sammen, og nu skal data så sættes op efter summen af dette, kode:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<?php
$con = mysql_connect("localhost","****","*****");
if (!$con)
  {
  die('Could not connect: ' . mysql_error());
  }

mysql_select_db("******", $con);

$query = "SELECT player, COUNT(vid), SUM(population) FROM x_world GROUP BY SUM(population) DESC";
   
$result = mysql_query($query) or die(mysql_error());

// Print out result

echo "<table border='1'>
<tr>
<th>Spiller</th>
<th>Byer</th>
<th>Indbyggere</th>
</tr>";

while($row = mysql_fetch_array($result))
  {
  echo "<tr>";
  echo "<td>" . $row['player'] . "</td>";
  echo "<td>" . $row['COUNT(vid)'] . "</td>";
  echo "<td>" . $row['SUM(population)'] . "</td>";
 
  echo "</tr>";
  }
echo "</table>";

mysql_close($con);
?>

Jeg får denne fejl melding:
"Invalid use of group function"