$arrProcuct_id=array();
$arrProduct_id=$_POST['pdf_order_id'];
if (count($arrProduct_id) > 0) {
    $where = $where." order_id in (";
    $rcnt = 0;
    foreach($arrProduct_id as $product_id) {
            if ($rcnt > 0) {
                $where = $where.",".$product_id;
        }else{
            $where = $where.$product_id;
            }
        $rcnt += 1;
    }
    $where = $where.")";
}else{
    $where = "1=1";
}