MySQL Update Issue

[motomania]

I'm not new to PHP but I don't claim to mbe an expert either. I'm having a problem with some check user code that also should update the users record with the datetime that they just logged in. I am sure that the db connection works fine as I use the same connection in numerous other pages for queries, etc. I'm sure this is probably something simple but the db doesn't get updated with the login datetime. If I refresh the page, then it does.

TIA for any help given. Here's the code

require_once ('mydb_connect.php');
// check if the user info validates the db
$sql = mysql_query("SELECT * FROM members WHERE username='$username' AND password='$password'");
$login_check = mysql_num_rows($sql);
if($login_check > 0){
 while($row = mysql_fetch_array($sql)){
 foreach( $row AS $key => $val ){
  $$key = stripslashes( $val );
 }
  // Register some session variables!
  $_SESSION['membernumber'] = $memnumber;
  $_SESSION['name'] = $username;
  $_SESSION['uid'] = $userid;
  $_SESSION['usarmlevel'] = $userlevel;

  mysql_close(); // Close the database connection.
 }
  date_default_timezone_set('America/Los_Angeles');
  $lastlogindatetime = date("Y-m-d H:i:s");

  include ('mydb_connect.php');
  $loginquery = "UPDATE members SET last_login='$lastlogindatetime' WHERE userid='$uid'";
  $result = mysql_query($loginquery);

  if ($result) {
  $dbok = True;
  } else {
    die('Invalid query: ' . mysql_error());
    sleep(10);
  }
  mysql_close(); // Close the database connection.
  include 'home.php';
} else {
 include 'loginerror.php';
}

[devinemke]

require_once('mydb_connect.php');

$result = mysql_query("SELECT * FROM members WHERE username = '$username' AND password = '$password'") or exit(mysql_error());
if (mysql_num_rows($result))
{
	$row = mysql_fetch_array($result);

$_SESSION['membernumber'] = $row['memnumber'];
$_SESSION['name'] = $row['username'];
$_SESSION['uid'] = $row['userid'];
$_SESSION['usarmlevel'] = $row['userlevel'];
}
else
{
	exit('no rows found matching that username / password');
}

date_default_timezone_set('America/Los_Angeles');
$lastlogindatetime = date('Y-m-d H:i:s');
$result = mysql_query("UPDATE members SET last_login = '$lastlogindatetime' WHERE userid = " . $_SESSION['uid']) or exit(mysql_error());