unset particular session in php code example

Example 1: php unset session variable

// Destroy a sesion variable name 'variable_name' 
<?php
unset($_SESSION['variable_name']);
?>

Example 2: unset session in php

session_unset();    //Destrol all session variables

Example 3: session value not removed php

All of a sudden neither session_destroy() nor $_SESSION=[] were sufficient to log out. I found the next to work:
<?php
setcookie(session_name(), session_id(), 1); // to expire the session
$_SESSION = [];
?>