使用GET时，旧数据会从POST中删除

So I am having an issue. I used POST to send data to a new page. I use get to send data to a function but it seems the POST data get wiped. Here some code to help explain.

POST CODE to send to form vieworder (works perfect!)

<form method="post" action="vieworder.php">
     <input type="hidden" name ="user_id" value="<?php echo $_SESSION['user_id']; ?>">
     <input type="hidden" name ="id" value="<?php echo $data1[$x]['id']; ?>">
     <input type="submit" name="submit" value="View"> </td>
</form>

So on the vieworder page I want used to be able to update the data using this form. This form works as well except i need that value "id" from the orginal post. It works and the "id"has the data until I use this form.

<form name="approveform" method="get" action="">
            Index Number*: <input type="text" name="IndexNum">&nbsp;
            <input type="submit" value="Approve" action="">
</form>

I would also prefer to use the POST method but using GET was my first solution to no deleting the data from POST.

Anyways I then just send the data to a function to update two fields.

Any way to get correct the code?

<?php
  $id=$_POST['user_id'];
?>

<form name="approveform" method="get" action="">
  Index Number*: <input type="text" name="IndexNum">&nbsp;
  <input type='hidden' value='<?php echo $id;?>'>
  <input type="submit" value="Approve" action="">
</form>