Как отсеять несуществующие товары?

function catalog(){
    $query = "SELECT * FROM categories ORDER BY category_id";
    $res = mysql_query($query) or die(mysql_query());
    
    // массив категорий
    $cat = array();
    while($row = mysql_fetch_assoc($res)){
        if(!$row['parent_id']){
            $cat[$row['category_id']][] = $row['category_name'];
        }else{
            $cat[$row['parent_id']]['sub'][$row['category_id']] = $row['category_name'];
        }
    }
    return $cat;
}

function product($category){
    $query = "(SELECT goods_id, name, img, price, old_price, hits, new, sale
        FROM goods 
            WHERE good_brandid = $category AND visible='1')
        UNION
        (SELECT goods_id, name, img, price, old_price, hits, new, sale
            FROM goods
                WHERE good_brandid IN
            (
                SELECT category_id FROM categories WHERE parent_id = $category
            ) AND visible='1')";
    $res = mysql_query($query) or die(mysql_error());
    
    $products = array();
    while($row = mysql_fetch_assoc($res)){
        $products[] = $row;
    }
    
    return $products;
}

function get_goods($goods_id){
    $query = "SELECT * FROM goods WHERE goods_id = $goods_id AND visible = '1'";
    $res = mysql_query($query);
    
    $goods = array();
    $goods = mysql_fetch_assoc($res);
    if($goods['img_slide']){
        $goods['img_slide'] = explode("|", $goods['img_slide']);
    }
    
    return $goods;
}

function get_goods($goods_id){
    $query = "SELECT * FROM goods WHERE goods_id = $goods_id AND visible = '1'";
    $res = mysql_query($query);
    
    $goods = array();
    $goods = mysql_fetch_assoc($res);
    if($goods['img_slide']){
        $goods['img_slide'] = explode("|", $goods['img_slide']);
    }
    if(empty($goods)){
        header ("HTTP/1.1 404 Not Found");
        header('Location:./404.php');
        exit();
    }
    return $goods;
}

    case('product'):
        // отдельный товар
        $goods_id = abs( (int)$_GET['goods_id'] );
        if($goods_id){
            $goods = get_goods($goods_id);
        }
    break;