<form action="enquete/page1.php" method="POST">
    <input type="hidden" name="x">
    <input type="submit" value="Go to Google">
</form>
<?php
    if(isset($_POST['x'])){
        $database->insert_user_id;
        header('Location: enquete/page1.php');
    }
?>


    function insert_user_id(){
            $sql = "INSERT INTO user "
        . "(user_id)"
        . "VALUES (user_id) ";
            $sth = $this->pdo->prepare($sql);
            $sth->execute();
    }