当点击高到低价格应该改变

想要按cat_id对价格进行排序，当从下拉类别中点击产品时，产品将在结果中打开.php页面，当单击从高到低时，它不会显示任何产品数据库。

功能.php

  function getcategoryPro(){
 if(isset($_GET['category'])){
$cat_id = $_GET['category'];
// SQL query to interact with info from our database
$get_category_pro = "SELECT * FROM products WHERE cat_id =$cat_id";
 if (isset($_GET['sortby'])) {
$sortby = $_GET['sortby'];
// SQL query to interact with info from our database
if ($sortby == 'pricehilo') {
$get_category_pro = "SELECT * FROM products WHERE cat_id =$cat_id ORDER BY price DESC";
}
elseif ($sortby == 'pricelohi') {
$get_category_pro ="SELECT * FROM products WHERE cat_id =$cat_id ORDER BY price ASC";
  }
 }  
 $run_category_pro= mysql_query($get_category_pro); 

   $count = mysql_num_rows($run_category_pro); 
 if($count==0){
  echo"<h2>no Products found in this category!";
            }   
   $dynamicList = '<table border="0" cellpadding="2">';
 while($row_products = mysql_fetch_array($run_category_pro)){ 
   $id = $row_products["id"];
   $product_name = $row_products["product_name"];
   $price=$row_products["price"];
   $date_added = strftime("%b %d, %Y",strtotime($row_products['date_added']));

   if ($i % 9 == 0) { // if $i is divisible by our target number (in this case "3")
    $dynamicList .= 
    '<tr><td><img style="padding:10px;/><a href="product.php?id=' . $id . '"><img 
  style="border: #000033 1px solid;" src="inventory_images/' . $id . '.jpg" 
  width="200" height="225" alt="' . $product_name . '"/><br/>
      <width="150" align="left" valign="top" scope="col">' . $product_name . '<br/>
      Rs.&nbsp;' . $price . '<br/>
      <a href="product.php?id=' . $id . '"><button>Buy Now</button></td>';

   } else {
    $dynamicList .= '<td><img style="padding:10px;/><a href="product.php?id=' . $id .
  '"><img style="border: #000033 1px solid;" src="inventory_images/' . $id . '.jpg" 
 width="200" height="225" alt="' . $product_name . '"/><br/>
      <width="150" align="left" valign="top" scope="col">' . $product_name . '<br/>
      Rs.&nbsp;' . $price . '<br/>
      <a href="product.php?id=' . $id . '"><button>Buy Now</button></td>';

    }
   $i++;
  }
  echo $dynamicList;
  $dynamicList .= '</tr></table>';
    }  
     }
    results.php
   <?php 
  getcategoryPro();
   ?>
    <p><a href="results.php?sortby=pricehilo">Price (Highest-Lowest)</a></p>
    <p><a href="results.php?sortby=pricelohi">Price (Lowest-Highest)</a></p>

当从下拉菜单单击手机时，此链接随产品一起提供

results.php?category=1

当我们单击从高到低时，此链接与味精一起打开在此类别中找不到产品

results.php?sortby=pricelohi

它应该是：

results.php?category=1&sortby=pricelohi