When selecting data from the database, the results are doubled, the same result is shown twice where is the error in the code?

Question

Backup

Here is the code. I can't figure out where the error is:

$sort='asc';
$sql = "SELECT * FROM open_product_prices, open_product_descriptions, open_products_categories, open_products WHERE open_product_prices.product_id = open_product_descriptions.product_id and open_product_prices.product_id = open_products_categories.product_id and open_product_prices.product_id = open_products.product_id and category_id=211 and list_price>0 ORDER BY price sort";
$result = mysql_query($sql) or die(mysql_error());
$table = "

vendor code	Name	Recom. price	Price PROMOTION	To order
".$product_code."	".$product."	".$list_price."	".$price."	To order

";
echo $table;