要添加到计数查询以显示分页的变量ID

I have been working on this all day and this is my second post today here. I have managed to create pagination and display the page numbers on certain pages. When I have introduced it to my products page I have struggled to add the variable ID cat_id. If I manually add a category ID it displays the first page but when I select the second it loses the list as the query doesn't contain the variable.

I have tried "SELECT COUNT(*) As Total FROM products WHERE prod_id = {$cat_id}" but do I then need to reference that in showproduct.php? It displays the paginated data but page list does not display and has error Undefined variable: cat_id. Whats the best way to define the variable here.

This is starting to frustrate me as it shouldn't have taken as long as it has and I still have jquery to add. Plus I know the mysql is outdated but I would like to get it working first.

So my question is how to add the {$cat_id} to the COUNT query.

showproduct.php

.......

    <p class="pagination">
<?php
    if(isset($page_num))
    {
        $result = mysql_query("SELECT COUNT(*) As Total FROM products WHERE prod_id = {$cat_id}");
        $rows = mysql_num_rows($result);
        if($rows)
        {
            $rs = mysql_fetch_array($result);
            $total = $rs["Total"];
        }
        $totalPages = ceil($total / $perpage);
        if($page_num <=1 )
        {
            echo '<span id="page_links" style="font-weight:bold;"> < </span>';
        }
        else
        {
            $j = $page_num - 1;
            echo '<span><a id="page_a_link" href="../anonymous/anonymous.master.php?page=showproduct.php&page_num=' . $j . '"> < </a></span>';
        }
        for($i=1; $i <= $totalPages; $i++)
        {
            if($i<>$page_num)
            {
                echo '<span><a href="../anonymous/anonymous.master.php?page=showproduct.php&page_num=' .$i. '" id="page_a_link">' . $i . '</a></span>';
            }
            else
            {
                echo '<span id="page_links" style="font-weight:bold;">' . $i . '</span>';
            }
        }
        if($page_num == $totalPages )
        {
            echo '<span id="page_links" style="font-weight:bold;">Next ></span>';
        }
        else
        {
            $j = $page_num + 1;
            echo '<span><a href="../anonymous/anonymous.master.php?page=showproduct.php&page_num=' .$j. '" id="page_a_link"> > </a></span>';
        }
    }
?>
</p>


......

Get Product.php

 .....

<?php
function get_posts($id = null, $cat_id = null) {
$posts = array();
$perpage = 8;
 if(isset($_GET["page_num"]))
 {
  $page_num = intval($_GET["page_num"]);
 }
 else
 {
  $page_num = 1;
 }
 if ($page_num < 1)
 {
   $page_num = 1;
 }
 $calc = $perpage * $page_num;
 $start = $calc - $perpage;

    $query ="SELECT  `products`.`id` AS  `name` ,  `products_cat`.`id` AS  `category_id` , `products`.`name` AS `title` ,  `description` ,  `price` ,  `sale` ,  `picture` 
FROM  `products` 
INNER JOIN  `products_cat` ON  `products`.`prod_id` =  `products_cat`.`id` ";

    if ( isset($id) ) {
    $id = (int) $id;
    $query .= " WHERE `products`.`id` = {$id}";
    }

    if ( isset($cat_id) ) {
        $cat_id = (int) $cat_id;
        $query .= " WHERE `products_cat`.`id` = {$cat_id}";
}

    $query .= " ORDER BY `products`.`price` DESC Limit $start, $perpage";

    $query = mysql_query($query);
    echo mysql_error();
    while ( $row = mysql_fetch_assoc($query) ) {
        $posts[] = $row;
        }

    return $posts;
}

....

Table View

CREATE TABLE `products` (
  `id` int(100) NOT NULL AUTO_INCREMENT,
  `prod_id` int(15) NOT NULL,
  `prod_sub_id` int(15) DEFAULT NULL,
  `description` varchar(3000) NOT NULL,
  `sale` varchar(100) DEFAULT NULL,
  `name` varchar(100) NOT NULL,
  `price` varchar(100) NOT NULL,
  `picture` varchar(100) NOT NULL,
  `timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=60 DEFAULT CHARSET=latin1