$warunki='';
if(isset($_POST['plec'])){
	$warunki .= ' AND (plec="'.$_POST['plec'].'")';
}
if(isset($_POST['wiek_od'])){
	$warunki .= ' AND (wiek BETWEEN '.$_POST['wiek_od'].' AND 100)';
}
if(isset($_POST['wiek_do'])){
	$warunki .= ' AND (wiek BETWEEN 0 AND '.$_POST['wiek_do'].')';
}
$users = mysql_query("SELECT * FROM users WHERE sesja<>''".$warunki." GROUP BY RAND() LIMIT 30");