这个pdo代码怎么了？ [关闭]

why is this pdo statement giving error? could someone help me with this?

if (isset($_POST["leerling"])) {
    $stmt = $conn->prepare("select * from cijfer where naam=naam");
    $stmt->bindParam(':naam', $naam);
    $klant = $_POST["leerling"];
    $stmt->execute();
    $stmt->setFetchMode(PDO::FETCH_ASSOC); 
    foreach ($stmt->fetchAll() as $row){
        echo "<tr>";
        echo "<td>" . $row["vak"] . "</td>";
        echo "<td>" . $row["naam"] . "</td>";
        echo "<td>" . $row["cijfer"] . "</td>";
        echo "</tr>";
    }
    $conn = null;
}

Change select * from cijfer where naam=naam to select * from cijfer where naam=:naam