通过php mysql中的单选按钮过滤价格

i am working on e-commerce website and in products section i want to give a function to sort product by price range like 100 to 500 but i have no idea to connect html radio button with mysql that on click product get sort on screen.

[enter image description here][1]

This is html code for radio button

<form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>" method="post">
  <ul class="radio">
  <li><input type="radio" name="radio" id="r1" value="radio"/>
  <label for="radio1">100-500</label></li>
 
  <li><input type="radio" name="radio" id="r2" value="radio2"/>
  <label for="radio2">600-1000</label></li>
  
  <li><input type="radio" name="radio" id="r3" value="radio"/>
  <label for="radio3">1100-1500</label></li>
  
  <li><input type="radio" name="radio" id="r4" value="radio4"/>
  <label for="radio4">1600-2000</label></li>
  
  <li><input type="radio" name="radio" id="r5" value="radio5"/>
  <label for="radio5">2100-2500</label></li>
  
  
  </ul>
  </form>

And this php and mysql code

<?php




$results1 = mysqli_query($db,"SELECT product_code, product_name, product_img_name, price FROM products where price> 500 ORDER BY id ASC");
if($results1){ 
$products_item = '<ul class="products">';

while($obj = $results1->fetch_object())
{
$products_item .= <<<EOT
    <li class="product">
    <form method="post" action="cart_update.php">
    <div class="product-content"><h3>{$obj->product_name}</h3>
    <div class="product-thumb"><img height="250px" src="../../img/{$obj->product_img_name}"></div>
    
    <div class="product-info">
    Price {$currency}{$obj->price} 
    
    <fieldset>
    
    <label>
        <span>size</span>
        <select name="product_color">
        <option value="Black">Medium</option>
        <option value="Silver">Small</option>
        </select>
    </label>
    
    <label>
        <span>Quantity</span>
        <input type="text" size="2" maxlength="2" name="product_qty" value="1" />
    </label>
    
    </fieldset>
    <input type="hidden" name="product_code" value="{$obj->product_code}" />
    <input type="hidden" name="type" value="add" />
    <input type="hidden" name="return_url" value="{$current_url}" />
    <div align="center"><button type="submit" class="add_to_cart">Add</button></div>
    </div></div>
    </form>
    </li>
EOT;
}

}

?>