<?php
if (isset($id)) {
$ids = implode(',', $id);

$database->setQuery( "SELECT * FROM #__rent"
	. "\nWHERE id IN(".$ids.")"
        . "\nORDER BY id ASC"
        );

        $rows = $database->loadObjectList();
        foreach ( $rows AS $row) {
         	
	 echo "<tr class='sectiontableentry1'>";
	 echo "<td align='center'>$row->id";
         echo "</td>";
	 echo "<td>$row->material";
         echo "</td>";
	 echo "<td>$row->category";
         echo "</td>";
	 echo "<td>$row->discription";
         echo "</td>";
	 echo "<td align='center'>$row->price";
         echo "</td>";
	 echo "<td align='center'>$row->disposit";
         echo "</td>";	
	 echo "</tr>";
	 } 
$query_price_count = "SELECT SUM (price) FROM #__rent  WHERE id  IN(".$ids.") ";
$database->setQuery( $query_price_count );
$total_price = $database->loadResult(); 
        echo $total_price;   //hier die Testausgabe

}

$database->setQuery( "SELECT * FROM #__rent"
   . "\nWHERE id IN(".$ids.")"
        . "\nORDER BY id ASC"
        );

---

$x->setQuery("SELECT
              FROM
              WHERE
              ORDER BY ");