How to set SESSION variables? (Beginner)

[Christophe27]

Hi,

I'm a beginner PHP programmer.

I use the following checkLogin.php script:

<?php 
session_start();
include '../config.php';

$username = $_POST['username'];

if ($_POST['Submit']=='Login')

{
$md5pass = md5($_POST['password']);
$sql = "SELECT username, password FROM users WHERE 
            username = '$username' AND 
            password = '$md5pass' AND 
            user_activated='1'"; 
            
$result = mysql_query($sql) or die (mysql_error()); 
$num = mysql_num_rows($result);

    if ( $num != 0 ) { 
		
        // A matching row was found - the user is authenticated. 
        
	   list($username,$md5pass) = mysql_fetch_row($result);
		// this sets variables in the session 
		$_SESSION['username']= $username;  		
			
		if (isset($_GET['ret']) && !empty($_GET['ret']))
		{
		header("Location: $_GET[ret]");
		} else {
		header( 'Location: /dashboard/' ) ;
		}
		//echo "Logged in...";
		exit();
    } 

header("Location: login.php?msg=Invalid Login");
//echo "Error:";
exit();		
}

?>

Question Now I'm wondering what to do to select the user_id as well from the database and store them in another SESSION variable?

THANK YOU

Best,
Christophe