<form class="Speichern" action = "" method = "POST">
<?php

    while ($zeile = mysqli_fetch_array($db_aus))
    {
        $zähler++;
        $name = "selectfield$zähler";

        echo "<tr>";
        echo "<td>". $zeile['S_Vorname'] ."</td>";
        echo "<td>". $zeile['S_Nachname'] . "</td>";
        echo "<td><select name='$name'>";
        echo "<option value='1'>Ja</option>";
        echo "<option value='2'>Nein</option>";
        echo "</select> </td>";
        echo "</tr>";
    }
    echo "</table>";
?>
<input type = "submit" value = "Speichern" name ="2"/>
<?php

    mysqli_free_result($db_aus);
    mysqli_free_result($db_class);

    if(isset($_POST['2']))
    {
        for($i = 1;$i <= $zähler; $i++)
        {
            $namen = "selectfield$i";
            if($_POST[$namen] == 2)
            {
                $füg = "INSERT INTO anwesenheit(A_ID,A_Fehlend,A_Entschuldigt,A_Datum,A_S_ID) VALUES ('null','1','null','$date','$i')";

                if($db->multi_query($füg) !== TRUE)
                {
                    echo "Error: " . $füg . "<br>" . $db->error;
                }

            }
        }

    }

?>
</form>