MySQL/PHP Auswahl nur eindeutiger Werte aus mehreren Spalten und Einfügen in separate Arrays

Wenn Sie es als eine SQL-Anweisung behalten möchten, können Sie:

$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'];
}