How to Protect from double posting insert MySQL

Submit once even the visitor is refresh the page from browser.
Here is the way to protect.
Use a SESSION.
1. Set a session in the form page

session_start();
$_SESSION[post_only_once] = 1;
echo "
 < form method=\"post\">
  Name < input type=\"text\" name=\"name\">
  < input type=\"submit\" value=\"submit\" name=\"submit\">
 < /form>
";

2. Check the session before doing INSERT into MySQL.

session_start();
if($_SESSION[post_only_once] == 1) {
  // here doing insert to mysql
}
unset($_SESSION[post_only_once]); // remove the session after insert