fetch uit meerdere DB werkt niet

<?php
$query = mysql_query("SELECT a.id, a.naam, a.gebruiker, b.id, b.gebruiker FROM gebruikers AS a, gebruikers_orders  AS b") or die(mysql_error());
echo "<select name=\"\">";
	while($fetch = mysql_fetch_array($query))
		{
		echo "<option value=\"\">".$fetch['naam']."</option>";
		}
echo "</select>";
			?>

<?php
$query = mysql_query("SELECT a.id, a.naam, a.gebruiker, b.id, b.gebruiker FROM gebruikers AS a, gebruikers_orders  AS b") or die(mysql_error());
echo "<select name=\"\">";
	while($fetch = mysql_fetch_array($query))
		{
		echo "<option value=\"\">".$fetch['naam']."</option>";
		}
echo "</select>";
			?>

<?php
$query = mysql_query("SELECT a.id, a.naam, a.gebruiker, b.id, b.gebruiker FROM gebruikers AS a, gebruikers_orders  AS b") or die(mysql_error());
while($fetch = mysql_fetch_array($query))
{
echo "<option value=\"".$fetch['a.naam']."\">".$fetch['a.naam']."</option>";
}
?>

<?php
$query = mysql_query("SELECT a.id, a.naam, a.gebruiker, b.id, b.gebruiker FROM gebruikers AS a, gebruikers_orders  AS b") or die(mysql_error());
while($fetch = mysql_fetch_array($query))
{
echo "<option value=\"".$fetch['a.naam']."\">".$fetch['a.naam']."</option>";
}
?>

SELECT a.id, a.naam, a.gebruiker
FROM gebruikers AS a
UNION SELECT b.id, b.gebruiker, NULL 
FROM gebruikers_orders AS b

SELECT a.id, a.naam, a.gebruiker
FROM gebruikers AS a
UNION SELECT b.id, b.gebruiker, NULL 
FROM gebruikers_orders AS b