<?php
$name = $_GET['name'];
try {
    $db = new PDO("mysql:dbname=app;host=localhost","root","passwort");
} catch(PDOException $e) {
    echo 'Feheler: ' . $e->getMessage();
    exit();
}
$sql = "SELECT id FROM users WHERE Name='$name'";
$cmd = $db->prepare($sql);
$cmd->execute();
while($zeile = $cmd->fetch(PDO::FETCH_OBJ)) {
    echo$zeile->id;
}
$db->exec($sql);

?>