Because you are limiting your query to 1 result, you don't actually need a while loop, so remove the while to leave you with this inside the if:
$row = mysql_fetch_array($sql);
$product_ name = $row["product_ name "];
$price = $row["price "];
You Should add 'or die(mysql_error())' to the end of your query to catch any errors.
Also, could you post your form code?