client_a_rappeler = ADDDATE(str_to_date('".$client_appele_le."', '%d/%m/%Y %H:%i:%s' ), INTERVAL 10 DAY),

Il faut changer la date dans le champs 1 puis cliquer sur submit
ENsuite il faut revenir sur le même formulaire et recliquer sur submit pour que le champs 2 soit updaté dans la base sql.

SELECT * FROM T_Client WHERE ADDDATE('date_dappel',10);
--ex :SELECT ADDDATE('2012-01-01', 10) afficherait 2012-01-11

<tr>
  <td>Client Appel&eacute; le <img src="images/arrow.gif" width="9" height="7" /></td>
  <td><input  name="client_appele_le" type="text" id="datepicker" value="<?php echo date('d/m/Y', strtotime($aff_donnee_client['client_appele_le']));?>"/></td>
  
  <?php 
$date_dappel = $aff_donnee_client['client_appele_le'];
$date_de_rappel = date('d/m/Y', strtotime($date_dappel.' +10 days'));
?>
  
  <td>Client &agrave; rapeller le <img src="images/arrow.gif" alt="" width="9" height="7" /></td>
  <td><input  name="client_a_rappeler" type="text" id="datepicker1" value="<?php echo $date_de_rappel;?>" /></td>
  <td colspan="5">&nbsp;</td>
</tr>

ça me met: 30/12/2012+10 day()

strtotime ("2012-12-30 +10 days") ; 

 echo "2012-12-30 +10 days (".strtotime ("2012-12-30 +10 days").")" ; 

<?php echo date('d/m/Y', strtotime($aff_donnee_client['client_a_rappeler']));?>

echo $_POST['client_a_rappeler']."+10 day" ; echo "(".strtotime($_POST['client_a_rappeler']."+10 day").")" ; 

$client_a_rappeler = date("Y-m-d", strtotime($_POST['client_a_rappeler']."+10 day"));

client_a_rappeler = (str_to_date('".$client_a_rappeler."' , '%d/%m/%Y %H:%i:%s' ))

$date = date("Y-m-d", strtotime("+10 day"));

<?php


//--------les includes des fonctions permettent le bon fonctionnement du site-------------- 
include "include_fns.php";
//-----------------------------------------------------------------------------------------
if ($_GET['type'] ='nouveau_client') {
$initiales_courtier = $_GET['initiales'];
$nom_courtier = $_GET['nom_courtier'];
$s_courtier = $_GET['s_courtier'];
}
else {
$initiales_courtier = $_POST['initiales_courtier'];
$nom_courtier = $_POST['username'];
}
echo $initiales_courtier ;
echo $nom_courtier ;


// ------------------------------- recuperation des variables -----------------------------
	$id = $_POST['id'];
	$ref_courtier = $_POST['ref_courtier'];
	
	$num_client = $_POST['num_client'];
	$num_rpa = $_POST['num_rpa'];
	$client_appele_le = $_POST['client_appele_le'];
	$client_a_rappeler = $_POST['client_appele_le'];
	
	

	$paiement_recu_le = $_POST['paiement_recu_le'];
	$echeance_rpa = $_POST['echeance_rpa'];
	$civilite = $_POST['civilite'];
	$nom = $_POST['nom'];
	$prenom = $_POST['prenom'];
	$rs = addslashes(trim($_POST['rs']));
	$telephone = $_POST['telephone'];
	$fax = $_POST['fax'];
	$mail = addslashes(trim($_POST['mail']));
	$adresse = addslashes(trim($_POST['adresse']));
	$complement_adresse = addslashes(trim($_POST['complement_adresse']));
	$cp = $_POST['cp'];
	$ville = addslashes(trim($_POST['ville']));
	$montant = $_POST['montant'];
	$observations = addslashes(trim($_POST['observations']));




	//$num_dossier = round(rand(0, time())/25000);
	//$num_saisie = round(time()/1500000);


//-----------------------------------------------------------------------------------------
// || !$_POST['telephone'] || !$_POST['adresse'] || !$_POST['code_postal'] || !$_POST['ville'] || !$_POST['num_siret']
//-------------- verifie la presence des variables sinon affiche message erreur -----------
if (!$_POST['ref_courtier']) {
   			    
	echo "<div id=\"message\">".IMPOSSIBLE_POURSUIVRE_SAISIE_INCOMPLETE." !<br />";
       	echo "<a href=\"ajouter_client.php\">".RETOUR."</a></div><br />";
//-----------------------------------------------------------------------------------------

//-------------------- affichage du bas de page et quitte le programme --------------------
    	include "bas.php";	
    	exit();
}
else {
//-----------------------------------------------------------------------------------------

//--------------------- connexion db requete sql sur table articles -----------------------
    $conn = db_connect();
//-----------------------------------------------------------------------------------------
 $time = time();
//-----------------------------------------------------------------------------------------
	if ($id) {
		
	$sql = "update ".CLIENTS." set 
	ref_courtier ='$ref_courtier',
	initiales_courtier = '$initiales_courtier',
	num_client = '$num_client',
	num_rpa = '$num_rpa',
	client_appele_le = (str_to_date( '".$client_appele_le."' , '%d/%m/%Y %H:%i:%s' )),
	client_a_rappeler = UNIX_TIMESTAMP(str_to_date( '".$client_a_rappeler."', '%d/%m/%Y %H:%i:%s' ))+ 10 * 24 *3600,
	echeance_rpa = '$echeance_rpa',
	civilite = '$civilite',
	nom = '$nom',
	prenom = '$prenom',
	rs = '$rs',
	telephone = '$telephone',
	fax = '$fax',
	mail = '$mail',
	adresse = '$adresse',
	complement_adresse = '$complement_adresse',
	cp = '$cp',
	ville = '$ville',
	montant = '$montant',
	observations = '$observations',
	modifier = '$time',
	username ='$nom_courtier',
	sexe_username = '$s_courtier',
	paiement_recu_le = (str_to_date( '".$paiement_recu_le."' , '%d/%m/%Y %H:%i:%s' ))
	where id = '$id'";

	$result = @mysql_query($sql, $conn) or die('Erreur SQL !'.$sql.'<br>'.mysql_error());

	}
		
	else {
 // vérification si utilisateur existe déjà
   $conn = db_connect();
   $sql1 = "select * from ".CLIENTS." where nom = '$nom' or telephone = '$telephone'"; 
   $resultat1 = mysql_query($sql1, $conn);
   $nbr = mysql_num_rows($resultat1);

   if ($nbr > '0') {
	echo "<div id=\"message\">".IL_Y_A." $nb Client du nom de <b>'$nom'</b> ou un num&eacute;ro de t&eacute;l&eacute;phone <b>'$telephone'</b> ".DEJA_UTILISE."<br />";
       	echo "[  <a href='javascript:history.go(-1)'>".RETOUR."</a>  ]</div><br />";

//------------------- affichage du bas de page et quitte le programme --------------------
  	include "bas.php";
  	exit();
   } 
   else {		
		
		//$num_client = round(rand(1500, time())/500000);
		//$username = $_SESSION["administrateur"] or $_SESSION["utilisateur"];
$sql = "insert into ".CLIENTS." values ('','$ref_courtier',
	'$initiales_courtier',
	'$num_client',
	'$num_rpa',
	'$echeance_rpa',
	'$rs',
	'$civilite',
	'$nom',
	'$prenom',
	'$adresse',
	'$complement_adresse',
	'$cp',
	'$ville',
	'$mail',
	'$telephone',
	'$fax',
	'$montant',
	'$observations',
	'$time', 
	'$time', 
	  NULL,
	 '$identite_courtier ',
	 '$sexe_courtier ',
	 (str_to_date( '".$client_appele_le."' , '%d/%m/%Y %H:%i:%s' ))),
	(str_to_date( '".$client_a_rappeler."' , '%d/%m/%Y %H:%i:%s' ))),
	 (str_to_date( '".$paiement_recu_le."' , '%d/%m/%Y %H:%i:%s' )))";
	}

		//$date_limite = (time()+(86400 * 364));
//		$sql_dossier = "insert into ".ENTREPRISES_DOSSIERS." values ('', '$num_dossier', '$date_limite', '$num_saisie', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '$num_client')";
//		$resultat_dossier = @mysql_query($sql_dossier, $conn);
	//}
		$result = @mysql_query($sql, $conn) or die('Erreur SQL !'.$sql.'<br>'.mysql_error());
}

//-----------------------------------------------------------------------------------------

//----------------------si la requete n'aboutie pas message erreur ------------------------
if (!$result) {
	echo "<div id=\"message\">".ERREUR_REQUETE." <PRE>$sql</PRE><br />";
       	echo "<a href=\"ajouter_client.php\">".RETOUR."</a></div><br />";
  exit();
}
//------------------------------------------------------------------------------------------

//------------------------------------------------------------------------------------------
    include "bas.php";	
  // echo "<meta http-equiv=\"refresh\" content=\"0;url=rechercher_client.php\" />";
  echo "<meta http-equiv=\"refresh\" content=\"0;url=rechercher_client.php\" />";
//------------------------------------------------------------------------------------------
}
?>