function pre_render($data)
{
	$rows = $_GET["jqgrid_page"] * $_GET["rows"];
	$sidx = $_GET['sidx']; // get index row - i.e. user click to sort
	$sord = $_GET['sord']; // get the direction
	
	// same sql as in select_command
	$rs = mysql_fetch_assoc(mysql_query("SELECT SUM(total) as s FROM (SELECT total FROM invheader ORDER BY $sidx $sord LIMIT $rows) AS tmp"));
	foreach($data["params"] as &$d)
	{
		$d["running_total"] = $rs["s"];
	}
}