我有3个表，产品，类别和prod_cat 产品的id和类别的id与prod_cat id_cat和id_prod相关。
我想显示某个类别的产品来展示它，所以我写了这段代码：
$cat=$_POST['cat'];
$sql = mysql_query("SELECT products.id, products.product_name, products_cat.prod_id FROM products
INNER JOIN products_cat ON products.id=products_cat.prod_id ORDER BY products.id");
$catCount = mysql_num_rows($sql); // count the output amount
while($row = mysql_fetch_array($sql)){
$id = $row["id"];
$product_name = $row["product_name"];
$price = $row["price"];
$date_added = strftime("%b %d, %Y", strtotime($row["date_added"]));
$prod_list .= "category ID: $id - <strong>$product_name</strong> <br />";
但是当我在页面上显示prod_list变量时它是空的，我做错了什么???
不过，我想这样显示：www.mydomain.com/show.php？cat = x