How to pass parameters in url using php page -

here trying pass id parameter next page using php.

i retrieving values database , have id primary key. want pass id next page. when pass parameter through url not appearing on url. how can this?

here have done.

echo "<a href='product-des.php?'". $row["product_id"].">"; 

here url visible till.php not able see id after that.

what doing wrong here... how can this?

to pass parameter

echo '<a href="product-des.php?pro_id='. $row["product_id"].'">'; 

to parameter:

echo $_get['pro_id'];