<?php
$user = "root"; // A adapté
$pass = "toor"; // A adapté
try {
    $sth = $dbh->prepare("SELECT Id_portes FROM Portes WHERE Batiment = 'Bat A'");
    $sth->execute();
    $result = $sth->fetchAll();
    print_r($result);
} catch (PDOException $e) {
    print "Erreur : " . $e->getMessage() . "<br/>";
    die();
}
?>