tri décroissant, fonctions sort() / rsort() ne fonctionnent pas

$sql = "select LOGIN,DATE_INSCRIPTION from utilisateurs ";
$res = mysql_query($sql);
while( $data = mysql_fetch_assoc($res) )
{
  $DateAjout = $data['DATE_INSCRIPTION'];
  $LogAjout = $data['LOGIN'];

  $Inscris = array($DateAjout);
  rsort($Inscris);
  foreach ($Inscris as $key => $val)
  {
    echo "Inscrit : [" . $key . "] = " . $val . "\n";
  }
}

select LOGIN,DATE_INSCRIPTION
from utilisateurs
order by DATE_INSCRIPTION desc
limit 0,4

$sql = "select LOGIN,DATE_INSCRIPTION from utilisateurs ";

$sql = "SELECT login, date_inscription FROM utilisateurs";

login | date_inscription
toto  | 20100306
titi  | 20100301
tutu  | 20100101

echo "Inscrit : [" . $key . "] = " . $val . "\n";

Notice: Undefined index: DATE_INSCRIPTION in /homepages/12/d311644604/htdocs/payetonju/www/index.php  on line 204

Notice: Undefined index: LOGIN in /homepages/12/d311644604/htdocs/payetonju/www/index.php on line 205

$sql = " SELECT login, date_inscription, STR_TO_DATE(DATE_INSCRIPTION, '%d/%m/%Y - %H:%i:%s') AS insdate FROM utilisateurs ORDER BY insdate DESC LIMIT 0,4";
$res = mysql_query($sql) or die('Erreur SQL ! <br />"<font color=\'red\'><b>'.$sql.'</b></font><br />'.mysql_error());
while( $data = mysql_fetch_assoc($res) )
{
  echo "- <b>".$LogAjout."</b> inscrit(e) le <b>".$DateAjout."</b><br />";
}

$DateAjout = $data['DATE_INSCRIPTION'];
$LogAjout = $data['LOGIN'];