<?php
$cases = array();
$referenceids = $_POST['ids']; // array(1, 2, 10, ...)
$orderCounter = 0;
foreach($referenceids as $rid)
{
$orderCounter++;
$cases[] = 'WHEN '.$rid.' THEN '.$orderCounter; // WHEN 1 THEN 1...
}
$query = 'UPDATE `table` SET `column` = CASE `referenceid` '.implode("\n", $cases).' END WHERE `referenceid` IN('. implode(',', $referenceids).')';
$result = mysql_query($query);
?>