function strToArray($string) {
   $result=array();
   for ($i=0;$i<=12;$i=$i+2) {
      
      $result[]=substr($string,$i,2);
   }
   return $result
}

function compareGrids($grid_player,$grid) {
     $nb_wrong=0;
     //attention cette comparaison fonctionne si l'ordre des numéros n a pas d importance.   
     $nb_wrong=count(array_diff($grid_player,$grid));
    
     /*en fait $nb_wrong contient le nombre de mauvais numéro ,c est pour cela que le nombre de bon numéro est égale à 6 moins le nombre de numéro qui diffèrent.   */
     return (6-$nb_wrong);
}

//select the grids played after last draw only
$query = ("SELECT * FROM grids_clients WHERE timeplayed BETWEEN $dateprevious AND $datecurrent");
$result = mysql_query($query) or die('Invalid query: ' . mysql_error());

//loop: load $data with one field of the array (will be used for comparaison with winning numbers
while ($return = mysql_fetch_assoc($result))
{
          //on reccupere le nombre de bon numéro 
          $rang=compareGrids( strToArray($return['grids_1']) , $grid );

         //on stocke le tout dans un tableau résultat
          $resultat[$return['id_client']]=array("rang"=>$rang,"grid"=>$return['grids_1']);
}
 
//ensuite tu peux parcourir le tableau resultat
while(list($id_player,$val)=each($resultat) ) {
      echo "idplayer:$id_player <br>";
      echo "grille jouée:".$val['grid']."<br>";
      echo "nombre de chiffre bon:".$val['rang']."<br>";
}

par contre le print_r ($temp); me retourne par exemple:
Array ( [0] => 021319212542 [1] => 122022303142 )

//select the grids played after last draw only
$query = ("SELECT * FROM grids_clients WHERE timeplayed BETWEEN $dateprevious AND $datecurrent");
$result = mysql_query($query) or die('Invalid query: ' . mysql_error());

//loop: load $data with one field of the array (will be used for comparaison with winning numbers
while ($return = mysql_fetch_assoc($result))
{
$id_clients[] = $return['id_clients'];
$temp[] = $return['grids_1'];
}

print_r($id_clients);
print_r($temp);

echo $data[$i];

// Construction de la requête
$query = "SELECT liste, des, champs FROM matable";
// Exécution de la requête
$result = mysql_query($query) or die('Invalid query: ' . mysql_error());

// Parcours des résultats de la requête
while ( $return = mysql_fetch_assoc($result); )
{
  // On ajoute la valeur de l'enregistrement courant dans un tableau global
  $data[] = $return['list'];
}

$query = ("SELECT date FROM grids_winning ORDER BY id_grids DESC LIMIT 1,1");
$result = mysql_query($query) or die('Invalid query: ' . mysql_error());

//store it into an array
// this will be useful in order to compare ONLY new grids for the current draw and diregards PREVIOUS grids
$dateprev = mysql_fetch_assoc($result);
$dateprevious = implode('',$dateprev);

//current date
$datecurrent = time();

//select the grids played after last draw only
$query = ("SELECT * FROM grids_clients WHERE timeplayed BETWEEN $dateprevious AND $datecurrent");
$result = mysql_query($query) or die('Invalid query: ' . mysql_error());

$counter = mysql_num_rows($result);

//load the variable with the array. fetch the array from query
$return = mysql_fetch_assoc($result);


//loop: load $data with one field of the array (will be used for comparaison with winning numbers)
for ($i = 0; $i < $counter; $i++)
{
$data[$i] = $return['grids_1'];
print_r($data[$i]);
}