PHP - product comparison table displaying only one column - php

Question

I am trying to compare products and display results in a table. I have a form page and a TABLE page, the problem is that when i select in the FORM page from the two drop-downs the same product(value) it will only display in the table one column and returns an multidimensional array containing one array not two arrays identical. When i select two different values from the from and submit, both selections are displayed. How can I avoid having one empty column if the user select the same product /ID ?
I was thinking maybe load the second drop down and subtracting from the list the value of the first drop down selection? I am not sure how to do it Or maybe there is an easier way like a form validation. Can someone show me how? Thanks
FORM.html
<?php
$products_dropdown = "select * from product_dp" ;
$statement = $dbh->prepare($products_dropdown);
$statement->execute();
$result_dp = $statement->fetchAll();?>
<form action="table.html" method="post">
<fieldset class="custimg">
<legend>Product Comparison</legend>
<div class="row">
<div class="large-block-grid-4"><br /></div>
<div class="large-block-grid-4">
<select name="id1" id="id1" class="small button secondary dropdown radius">`
<?php foreach ($result_dp as $row){
echo "<option value='".$row['id']."'>".$row['sku']."</option>";}?>
</select>
</div>
<div class="large-block-grid-4">
<select name="id2" id="id2" class="small button secondary dropdown radius">
<?php foreach ($result_dp as $row){
echo "<option value='".$row['id']."'>".$row['sku']."</option>"; }?>
</select>
<input type="submit" value="Compare" class="tiny button secondary" />
</div>
</div>
Table.html
$id1 = $_POST[id1];
$id2 = $_POST[id2];
$statement = $dbh->prepare("select * from products_specs where id IN ($id1,$id2)");
$statement->execute(array(':id1' => $id1, ':id2'=> $id2));
$statement->setFetchMode(PDO::FETCH_ASSOC);
$subrows = $statement->fetchAll();
print_r($subrows);
$yes = '<img src="images/icons/yes.png" width="16" height="16" />';
$no = '<img src="images/icons/no.png" width="16" height="16" />';?>
<table >
<thead>
<tr>
<th width="100"></th>
<th width="275"><?php echo $subrows[0][image]; ?></th>
<th width="275"><?php echo $subrows[1][image]; ?></th>
</tr>
<tr text-align="center">
<th width="100"></th>
<th class="centered-cell1"><font color="#990000"><?php echo "ID"." ".$subrows[0][id]; ?></th>
<th class="centered-cell1"><font color="#990000"><?php echo "ID"." ".$subrows[1][id]; ?></th>
</tr>
</thead>
<tbody>
<tr>
<td > Capacity </td>
<td align="center"><?php echo $subrows[0][capacity]; ?> </td>
<td align="center"><?php echo $subrows[1][capacity]; ?> </td>
</tr>
<tr>
<td > Memory </td>
<td align="center"><?php echo $subrows[0][mem]; ?> </td>
<td align="center"><?php echo $subrows[1][mem]; ?> </td>
</tr>
ect....

Answer 1

Very simple solution. After executing query use code:
if (!isset($subrows[1]))
$subrows[1] = $subrows[0];
Let users compare a product with itself if they want it.