ชำระค่างวด เงินกู้ อยากให้อัพเดตยอดคงเหลือของหมายเลขบัญชีนั้น php ช่วยดู code หน่อยค่ะ

<?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

$now = date('d-m-') . (date('Y')+543);
$time = date("G:i:s"); //เผื่ออยากใส่วันเวลาคนละช่อง
$sum = $l_loan - $ol_money ;
//$sum2 = $sum * $ol_money ;
$status = ("ชำระแล้ว");
if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
  $insertSQL = sprintf("INSERT INTO order_loan (l_id, ol_lastdate, ol_time, l_loan, i_interest, ol_interest, ol_money, ol_total,ol_balance, l_status) VALUES ('$l_id', '$now', '$time', '$l_loan', '$i_interest', '$ol_interest', '$ol_money', '$ol_total','$sum', '$status')");
                      

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

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

 <? //โค้ดหาผลรวม ?>
     <script language="javascript">
	 function sum()
	 {
	var l_loan = document.form1.l_loan.value;
	var i_interest = document.form1.i_interest.value;
	document.form1.ol_interest.value = l_loan * i_interest / 100
	}
    </script>
    
    <script language="javascript">

		function sum2(){
		var t1;
		var t2;
		var sum;
		t1=parseFloat(document.form1.ol_interest.value);
		t2=parseFloat(document.form1.ol_money.value);
		sum=t1+t2;
		document.form1.ol_total.value=sum;
		}
		</script>
    
    <form action="<?php echo $editFormAction; ?>" method="post" name="form1" id="form1">
  <table align="center">
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">รหัสบัญชีเงินกู้:</td>
      <td><input type="text" name="l_id" value="" size="32" style="background: #C0F9BD"/></td>
    </tr>
   
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">จำนวนเงินกู้:</td>
      <td><input type="text" name="l_loan" value="" size="32" style="background: #C0F9BD" onkeyup="sum()" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">อัตราดอกเบี้ยเงินกู้:</td>
      <td><input type="text" name="i_interest" value="" size="32" style="background: #C0F9BD" onkeyup="sum()" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">จำนวนดอกเบี้ยเงินกู้:</td>
      <td><input type="text" name="ol_interest" value="" size="32" style="background: #C0F9BD" onkeyup="sum2()" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right">จำนวนเงินที่ชำระค่างวด:</td>
      <td><input type="text" name="ol_money" value="" size="32" style="background: #C0F9BD" onkeyup="sum2()" /></td>
    </tr>
    <tr valign="baseline">
      <td nowrap="nowrap" align="right"> รวมทั้งสิ้น:</td>
      <td><input type="text" name="ol_total" value="" size="32" style="background: #C0F9BD" /></td>
    </tr>
    
   <tr valign="baseline">
          <td nowrap="nowrap" align="right"><input type="reset" name="button" id="button" value="Reset" /></td>
          <td><input type="submit" value="เพิ่มข้อมูล" />
          <a href="payment_correct.php">
        <input type="button" name="edit" value="แก้ไขข้อมูลชำระค่างวด" />
        </a></td>
        </tr>
  </table>
  <input type="hidden" name="MM_insert" value="form1" />
</form>