<?php
include("config.php");

$query = "SELECT tours.Id, tours.Name FROM tours JOIN dates ON tours.Id = dates.TourId AND dates.StartDate > '2012-12-31' WHERE Hide = '1' ORDER BY tours.Id";
$result = mysql_query($query);

$oldid = 0;

while ($row = mysql_fetch_array($result)) {
    if ($row['Id'] != $oldid) {
        echo $row['Id'] . "<br>\n";
        unhide($row['Id']);
        $oldid = $row['Id'];
    }
}

function unhide($id) {
    mysql_query("UPDATE tours SET Hide='0' WHERE Id = '" . $id . "' LIMIT 1");
}
?>