MySQL/PHP Selecionando apenas valores únicos de várias colunas e colocando-os em arrays separados

$sql = "
    SELECT DISTINCT 'make' as descr,make as val FROM items
    UNION
    SELECT DISTINCT 'model' as descr,model as val FROM items
    UNION
    SELECT DISTINCT 'year' as descr,year as val FROM items
    UNION
    SELECT DISTINCT 'month' as descr,month as val FROM items
    UNION
    SELECT DISTINCT 'day' as descr,day as val FROM items
    UNION
    SELECT DISTINCT 'hour' as descr,hour as val FROM items";

$result = @mysql_query($sql, $con) or die(mysql_error());

while($row = mysql_fetch_array($result)) {
    $make_array[$row['descr']][]=$row['val'];
}