How to submit/save to DB the cell's input data in dynamically added rows on a table using javascript /php

I can't get the input data inside the text boxes which are present inside the newly added dynamic rows in the table. Please note that the dynamic row adding is not only on the last row of the table but just below row where the the add button is present.

  `while($rows = mysql_fetch_array($result))
    {

    echo '<td>'.$rows["id"].'</td>
    <td id"].'">'.$rows["item"].'</td>
    <td id"].'">'.$rows["cost"].'</td>

   <td>
   <div id="addinput">
    <p>
  <button name="add" onclick="myFunction(this)" value="'.$btn_count.'">        <fontcolor="#FF0000" size="4">+</font></button>
</p>
</div>
</td>


<script>
function myFunction(y)
 {

  var f = y.parentNode;
  var d = f.parentNode;
  var g = d.parentNode;
  var c =g.parentNode.rowIndex;  
  var table = document.getElementById("myTable");
  var row = table.insertRow(c+1);


  var cell1 = row.insertCell(0);
  var cell2 = row.insertCell(1);

  var cell7 = row.insertCell(6);
  cell1.innerHTML = "<form name=frm_add action='index.php' method='POST' ><input  type=text name=txt_id size=10 placeholder=Id>";
  cell2.innerHTML = "<input type=text name=txt_item id=item_name size=10  placeholder=Item >";
cell3.innerHTML = "<input type=text name=txt_cost size=10 placeholder=0.00>";
cell4.innerHTML = "<input type=text name=txt_wp size=10 placeholder=0.00>";
cell5.innerHTML = "<input type=text name=txt_rp size=10 placeholder=0.00>";

cell6.innerHTML = "<input type='submit' name='submit_adding' value='Save11' size=10 >
</form>";

document.getElementById("myTable");
}
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after this iwrote the below code to submit the input text boxes data into DB

<?php
   if(isset($_POST['submit_adding']))
    {
     $item=$_POST['txt_item'];
     $cost=$_POST['txt_cost'];
     $wp=$_POST['txt_wp'];
     $rp=$_POST['txt_rp'];

     $q= $_POST['q'];

      if($p > 0)
       {
         $sql = "insert into shop".$q."_products (item,cost,wp,rp)values('$item','$cost','$wp','$rp')";
       }
         else
          {
           $sql = "insert into shop".$q."_products (item,cost,wp,rp)values('$item','$cost','$wp','$rp')";
          }
  mysql_query($sql); 
  ?>


<script>
alert("Successfully Added !!");
window.location.href="index.php?p=<?php echo $q;?>";
window.location.href="index.php";

</script>`
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but its not working..