ช่วยผมดู code ระบบรับชำระค่างวดหน่อยครับ มันคำนวนผิด

<?php require_once('Connections/satcha.php'); ?>
<?php
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "")
{
  if (PHP_VERSION < 6) {
    $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;
  }

  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? doubleval($theValue) : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
  $editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);
}
mysql_query("SET NAMES UTF8");
mysql_query("SET character_set_results=utf8");//ตั้งค่าการดึงข้อมูลออกมาให้เป็น utf8
mysql_query("SET character_set_client=utf8");//ตั้งค่าการส่งข้อมุลลงฐานข้อมูลออกมาให้เป็น utf8
mysql_query("SET character_set_connection=utf8");//ตั้งค่าการติดต่อฐานข้อมูลให้เป็น ut
if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
	
$now = (date("Y") + 543) . date("-m-d");
$time = date("G:i:s"); //เผื่ออยากใส่วันเวลาคนละช่อง
$cal_balance=(double)$_POST['l_loan']  -  (double)$_POST['ol_money'];
  
  $insertSQL = sprintf("INSERT INTO order_loan (l_id, ol_lastdate, ol_time, l_loan,i_interest,ol_interest, ol_money,ol_total,ol_balance, l_status) VALUES (%s, substr(now(),1,10),substr(now(),12,19), %s,%s, %s, %s, %s, %s, 'ชำระแล้ว')",
                       GetSQLValueString($_POST['l_id'], "text"),
                       GetSQLValueString($_POST['l_loan'], "double"),                       
                       GetSQLValueString($_POST['i_interest'], "double"),
                       GetSQLValueString($_POST['ol_interest'], "double"),
                       GetSQLValueString($_POST['ol_money'], "double"),
                       GetSQLValueString($_POST['ol_total'], "double"),



                       GetSQLValueString($cal_balance, "double"));
                       

  mysql_select_db($database_satcha, $satcha);
  $Result1 = mysql_query($insertSQL, $satcha) or die(mysql_error());

  $insertGoTo = "payment.php";
  if (isset($_SERVER['QUERY_STRING'])) {
    $insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
    $insertGoTo .= $_SERVER['QUERY_STRING'];
  }
  header(sprintf("Location: %s", $insertGoTo));
}
?>

<?php require_once('Connections/satcha.php'); ?>
<?php

$l_id=$_POST['l_id'];


$sql="select o.l_loan,sum(l.ol_money) as pay,l.l_loan-sum(l.ol_money) as sum 
from order_loan l RIGHT JOIN loan o on o.l_id=l.l_id
  where o.l_id='$l_id' group by o.l_id   ";
 // echo $sql;
  mysql_select_db("satcha", $satcha);
  $result = mysql_query($sql, $satcha) or die(mysql_error());

  while($row = mysql_fetch_array($result)){
  	if ($row['sum']==null) {
  		echo $row["l_loan"];
  	}else{
  		echo $row["sum"];
  	}
  	
  }

?>