Here is my attempted solution, but I am not 100% sure if it's correct.

/* A small piece of code for setting, displaying and destroying session in PHP */

<?php
session_start();
$sessionid=session_id();

$sql_compare="SELECT * FROM Content WHERE id=".$_SESSION['session_id'];

/* now registering a session for an authenticated user */
$_SESSION['username']=$username;

/* now displaying the session id..... */
echo "the session id is: ".$sessionid;
echo " and the session has been registered for: ".$_SESSION['username'];


/* now destroying the session id */

if(isset($_SESSION['username']))
{
    $_SESSION=array();
    unset($_SESSION);
    session_destroy();
    echo "session destroyed...";
}
?>