MySQL, PHP - Dynamisches Dropdown

<form method="POST">  
	<?php
		include 'dbconnect.php';  
		$i = 1;
		$filterabfrage = "SELECT * FROM tablename WHERE abteilung = '".$filter."'"." order by name";  
	
		$result = $db->query($filterabfrage);
			if (!$result)
		{
			die('Der Query konnte nicht ausgef&uuml;hrt werden: '.$db->error);  
		}
		if ($result->num_rows)
		{
		echo '<select size="1" name="namefilter" onchange=submit()>';  
		echo '<option value="0">Alle</option>';  
			while ($row = $result->fetch_assoc())
			{
		echo '<option value='.$i.'>'.($row['name']).'</option>';  
			$i=$i+1;
			}
		}

		?>
		</select>
		<br><br>
	<br>
	</form>
<?php
	if(isset($_POST["namefilter"]))  
	{
		//??????????????
	}
?>

if($filter == "" && $namefilter == "")  
{
		$abfrage = "SELECT sonstiges, id, abteilung, name, betrieb, art, DATE_FORMAT(von, '%d.%m.%Y') AS von, DATE_FORMAT(bis, '%d.%m.%Y') AS bis FROM praktikum  
                                      ORDER BY abteilung, name";  
		$stand = "SELECT MAX(stand) FROM praktikum";  
	} else if($namefilter == ""){  
		$abfrage = "SELECT sonstiges, id, abteilung, name, betrieb, art, DATE_FORMAT(von, '%d.%m.%Y') AS von, DATE_FORMAT(bis, '%d.%m.%Y') AS bis FROM praktikum  
                                      WHERE abteilung = '".$filter."'"." ORDER BY abteilung, name";  
		$stand = "SELECT MAX(stand) FROM praktikum";  
	} else if($namefilter != ""){  
		$abfrage = "SELECT sonstiges, id, abteilung, name, betrieb, art, DATE_FORMAT(von, '%d.%m.%Y') AS von, DATE_FORMAT(bis, '%d.%m.%Y') AS bis FROM praktikum  
                                      WHERE  name = '".$namefilter."'"." ORDER BY betrieb";  
		$stand = "SELECT MAX(stand) FROM praktikum";  
	}
.....