$col = array();
$col["title"] = "Total ordered";
$col["name"] = "total_order";
$col["search"] = true;
$col["editable"] = false;
$cols[] = $col;

// running total calculation
$e = array();
$e["on_data_display"] = array("pre_render","",true);
$g->set_events($e);

function pre_render($data)
{

       foreach($data["params"] as &$d)
    {
        $mid = $d["material_id"];
        $rs = mysql_fetch_assoc(mysql_query("SELECT SUM(material_quantity) as s FROM orders WHERE orders.material_id = $mid "));
        $d["total_order"] = $rs["s"];
    }
}