$sql="SELECT marche.*, categorie.ordinecategoria FROM marche LEFT JOIN categorie USING (idcategoria) ";
if ($_GET[idnegozio]) $sql.=" WHERE negozi LIKE '%$_GET[idnegozio]%' ";
$sql.=" ORDER BY ordinecategoria, nomemarca";
$Dbr=mysql_query($sql);
while ($row = mysql_fetch_array($Dbr)) {?>
} ?>