ขอคำแนะนำหน่อยครับ php เขียน select ฐานข้อมูล mysql แล้วทำการ Update โดย ลบค่าใน felds นั้น โดยใช้ Where

<?php 
session_start();
ob_start();

$ProductID=$_POST['ProductID'];
echo $ProductID;

$BillNo=$_POST['BillNo'];
echo $BillNo;

$QTY=$_POST['QTY'];
echo $QTY;
include("include/db_connect.php");
include("include/function.php");
if((isset($_SESSION['login_true_administrator'])) or (isset($_SESSION['login_true_AdminID'])))
{	
	
?>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link href="css/textcss.css" type="text/css" rel="stylesheet" >
<link href="css/styleinput.css" type="text/css" rel="stylesheet" >
<link href="css/stylelink.css" type="text/css" rel="stylesheet">
<form action="#" method="post" enctype="multipart/form-data" name="frm">
<?php 
$selectBill="SELECT * FROM stock_d.bill_out WHERE BillNo ='$BillNo'";
$sqlBill=mysql_query($selectBill)or die ("Show Error ::".mysql_error());

if(isset($sqlBill)){
		$selectmain="SELECT * FROM stock_d.stock_main WHERE ProductID='$ProductID'";
		$Qrymain=mysql_query($selectmain) or die("Error select main that:".mysql_error());
		while($Rowsed=mysql_fetch_array($Qrymain)){
			$proID=$Rowsed['ProductID'];
			$main=$Rowsed['StockMain'];
			}
			
		if(isset($Qrymain)){
			$main=$StockMain-$QTY;
			if(isset($main))
			
			{
				$updating=mysql_query("UPDATE  stock_d.stock_main SET 
				StockMain ='$main'  
				WHERE stock_main.ProductID ='$ProductID' 
				") or die("update faild that:".mysql_error());
				echo "<meta http-equiv='refresh' content='0;url=out_bill.php'>";
		echo "<script>alert('ບັນທຶກຂໍ້ມູນຮຽບຮ້ອຍແລ້ວ !!!');</script>";	
			}
			
			}
			else{ echo "No Main!!"; }		
	}
?>

<table  width="81%" border="1" align="center"cellpadding="1" cellspacing="0" bordercolor="#CCCCCC" style='BORDER-COLLAPSE: collapse'>
  <tr>
    <td colspan="5">ຄົ້ນຫາ <img src="img/zoom_in.png" width="16" height="16"><input type="search" id="BillNo" name="BillNo">&nbsp;&nbsp; <input name="search" type="submit" id="search" value="search"></td>
    </tr>
  <tr>
    <td>BillNo:</td>
    <td>ProductID/ລະຫັດເຄື່ອງ</td>
    <td>Name/ຊື່</td>
    <td>NameLao/ຊື່ລາວ</td>
    <td>QTY/ຈຳນວນ</td>
  </tr>
  <?php 
  $i =0;
  while($row=mysql_fetch_array($sqlBill))
  {
	  $i = $i + 1;
  ?>
  <tr>
    <td><?php echo $row['BillNo']; ?></td>
    <td><input type="text" name="ProductID<?php echo $i;?>" value="<?php echo $row['ProductID']; ?>" /></td>
    <td><input type="text"  name="Name<?php echo $i;?>"  value="<?php echo $row['Name']; ?>" /></td>
    <td><input type="text" name="NameLao<?php echo $i;?>" value=" <?php echo $row['NameLao']; ?>" /></td>
    <td><input type="text" name="QTY<?php echo $i;?>" id="QTY"value="<?php echo $row['QTY']; ?>" /></td>
  </tr>
  <?php } ?>
  <tr>
    <td colspan="5"  align="center"><input type="submit" name="delete" id="delete" value="Cut Stock"> &nbsp;&nbsp; <input type="reset" name="reset" id="reset" value="reset">
     </td>
    </tr> 
</table>

<?php 

		
?>

<?php }?> 
</form>
<?php
ob_end_flush();
mysql_close($d1,$db1,$c1);
mysql_close($d2,$db2,$c1);

exit();
?>

<?php
$hostname1="localhost";
$username1="root";
$password1="44@44";
$db1="stock_d";
$db2="staffdata";

$c1=mysql_connect($hostname1,$username1,$password1,"TRUE");
$d1=mysql_select_db($db1,$c1)or die((mysql_error));
$d2=mysql_select_db($db2,$c1)or die((mysql_error));

mysql_query("SET NAMES 'utf8'",$c1);
set_time_limit(0);
if(!$c1){
	echo "( ERROR : Connect Server $hostname1 !!!)";
	exit();
	
}else if(!$d1){
	echo "( ERROR : Connect MySql Server $db1 !!!)";
	exit();	
}else if(!$d2){
	echo "( ERROR : Connect MySql Server $db2 !!!)";
	exit();		
}

//====================================================
foreach($_GET as $varname=>$varvalue){
	if(empty($varvalue)){
		$empty[$varname]=$varvalue;
	}else{
		$get[$varname]=$varvalue;
	}
	$$varname=$varvalue;
}
foreach($_POST as $varname=>$varvalue) {
	if(empty($varvalue)){
		$empty[$varname]=$varvalue;
	}else{
		$post[$varname]=$varvalue;
	}
	$$varname=$varvalue;
}
//====================================================
?>

-------------
CREATE TABLE IF NOT EXISTS `bill_out` (
  `CodeOut` int(10) NOT NULL AUTO_INCREMENT,
  `BillNo` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `ProductID` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `Name` varchar(50) COLLATE utf8_unicode_ci NOT NULL,
  `NameLao` varchar(50) COLLATE utf8_unicode_ci NOT NULL,
  `QTY` int(255) NOT NULL,
  `KindID` varchar(10) COLLATE utf8_unicode_ci NOT NULL,
  `Remark` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
  PRIMARY KEY (`BillNo`,`ProductID`),
  UNIQUE KEY `CodeOut` (`CodeOut`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=3 ;

--
-- dump ตาราง `bill_out`
--

INSERT INTO `bill_out` (`CodeOut`, `BillNo`, `ProductID`, `Name`, `NameLao`, `QTY`, `KindID`, `Remark`) VALUES
(1, 'IT-00001', 'BE-00001', 'COFFEE', 'ກາເຟ', 1, 'ຖົງ', ''),
(2, 'IT-00001', 'BE-00002', 'SUGER', 'ນ້ຳຕານ', 1, 'ຖົງ', '');
------------------------------
-- phpMyAdmin SQL Dump
-- version 3.2.0.1
-- http://www.phpmyadmin.net
--
-- โฮสต์: localhost
-- เวลาในการสร้าง: 
-- รุ่นของเซิร์ฟเวอร์: 5.1.37
-- รุ่นของ PHP: 5.3.0

SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";

--
-- ฐานข้อมูล: `stock_d`
--

-- --------------------------------------------------------

--
-- โครงสร้างตาราง `stock_main`
--

CREATE TABLE IF NOT EXISTS `stock_main` (
  `StockMainID` int(10) NOT NULL AUTO_INCREMENT,
  `ProductID` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `Name` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
  `NameLao` varchar(50) COLLATE utf8_unicode_ci DEFAULT NULL,
  `StockMain` int(255) DEFAULT NULL,
  `DateStockMain` date DEFAULT NULL,
  PRIMARY KEY (`ProductID`),
  UNIQUE KEY `StockMainID` (`StockMainID`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=576 ;

--
-- dump ตาราง `stock_main`
--

INSERT INTO `stock_main` (`StockMainID`, `ProductID`, `Name`, `NameLao`, `StockMain`, `DateStockMain`) VALUES
(160, 'OS-00061', 'INK FOR STAMP/RED', 'ນ້ຳມືກໃສ່ແຜ່ນຈຳ', 100, '2017-05-12'),
(159, 'OS-00011', 'BLACK CLIP MIDDLE/NO:109', 'ກິບດຳເບ109', 100, '2017-05-12'),
-----------------------