ขอถามเกี่ยวกับการค้นหาข้อมูล เมื่อมีการเพิ่มข้อมูลโดยการใช้ checkbox กับ session คับ

<?php
session_start();

						
						 include("connect.ua");

						   $conn = mysqli_connect($serverName,$userName,$userPassword,$dbName);

							$sql = "SELECT * FROM producttest  ORDER BY ProductID ASC LIMIT 0,75 ";
							$query = mysqli_query($conn,$sql);
						?>	
						<table class="table no-margin">
							<thead>
							<tr>
								<td width="50">ภาพ</td>
								<td width="50">ลูกค้า</td>
								<td width="50">รหัส</td>
								<td width="100">ชื่อสินค้า</td>
								<td width="50">ราคา</td>
								<td width="100">จำนวน</td>
							</tr>
							</thead>
							<tbody>
						  <?php
						  while($result = mysqli_fetch_array($query,MYSQLI_ASSOC))
						  {
						  ?>
						<tr>
						<form class="form-horizontal" method="POST" action="customerorder.php" role="form">
							<td><input type="hidden" value="<?php echo $result["ProductID"];?>"><img src="img/<?php echo $result["Picture"];?>" width="40" height="40"></td>
							<td><?php echo $result["c_name"];?></td>
							<td><?php echo $result["Barcode"];?></td>
							<td><?php echo $result["ProductName"];?></td>
							<td><div align="center"><?php echo $result["Price"];?></div></td>
 						   <td><input type="hidden" name="txtProductID" value="<?php echo $result["ProductID"];?>" size="1"><input type="hidden" name="txtBarcode" value="<?php echo $result["Barcode"];?>" size="1"> <input type="text" name="txtQty" value="1" size="2"> <button type="submit" class="btn btn-success btn-sm"><i class="glyphicon glyphicon-plus"></i></button></td>
						</form>
						</tr>
						  </tbody>
						  <?php
						  }
						  ?>
						</table>
						<?php
						mysqli_close($conn);
						?>
						
						//หน้า customerorder.php				
						<?php
						ob_start();
						session_start();
							
						if(!isset($_SESSION["intLine"]))
						{
							if(isset($_POST["txtProductID"]))
							{
								 $_SESSION["intLine"] = 0;
								 $_SESSION["strProductID"][0] = $_POST["txtProductID"];
								 $_SESSION["strQty"][0] = $_POST["txtQty"];
							header("location:customerorder.php");
							}
						}
						else
						{
							$addcus = array_search($_POST["txtProductID"], $_SESSION["strProductID"]);
							if((string)$addcus != "")
							{
								 $_SESSION["strQty"][$addcus] = $_SESSION["strQty"][$addcus] + $_POST["txtQty"];
							}
							else
							{
								
								 $_SESSION["intLine"] = $_SESSION["intLine"] + 1;
								 $intNewLine = $_SESSION["intLine"];
								 $_SESSION["strProductID"][$intNewLine] = $_POST["txtProductID"];
								 $_SESSION["strQty"][$intNewLine] = $_POST["txtQty"];
							}
							header("location:customerorder.php");
						}
						?>