无法管理显示类别中的产品在PHP

Question

<?php 
// This block grabs the whole list for viewing
include "storescripts/connect_to_mysql.php";
$cat=$_POST['cat'];
$sql = mysql_query("select * from categories,products_cat,products where categories.id=products_cat.cat_id and products.id=products_cat.prod_id and categories=$cat");
$catCount = mysql_num_rows($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 />";
    }

?>

我有这三个表：1）产品表：id，product_name，price，category，subcategory

2）分类表：id，cat

3）products_cat表：cat_id，prod_id

我无法显示用户将从命令行cat = x输入的某些类别的产品，这只会给我这个错误：

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/perzul12/public_html/beta/show.php on line 6

Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /home/perzul12/public_html/beta/show.php on line 7

请帮我 ！ 这是我一个月唯一的金钱资源，我做不到！

Answer 1

此处的工作不在不推荐使用的mysql_函数中。 而是，您尚未返回有效的结果集。 尝试这个。

"select products_cat.products, categories.* 
from categories,
left join products_cat on products_cat.cat_id=products.id
where categories={$cat}"