UNIX_TIMESTAMP(ADDDATE(FROM_UNIXTIME(`tbl_croisiere`.`depart`, '%Y-%m-%d %H.%i.%s'), INTERVAL `tbl_croisiere`.`nuits` DAY)) AS `arrivee`

"SELECT ADDDATE(date_test, INTERVAL nuits DAY) AS resultat FROM test_date";

CREATE TABLE IF NOT EXISTS `test_date` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `DATE_TEST` date NOT NULL,
 `nuits` int(2) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ;

CREATE TABLE IF NOT EXISTS `test_date` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `DATE_TEST` date NOT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ;

--
-- Contenu de la table `test_date`
--

INSERT INTO `test_date` (`ID`, `DATE_TEST`) VALUES
(1, '2011-03-22');

$Ajout_jour = 5;

$sql = "SELECT ADDDATE(date_test, INTERVAL $Ajout_jour DAY) AS resultat FROM test_date";
$req = mysql_query($sql) or die('Erreur SQL !'.$sql.'<br>'.mysql_error());

$data = mysql_fetch_object($req);

echo $data->resultat;