Update WP user_login via SQL

gistfile1.php

<?php
// Force update our username (user_login)
global $wpdb;	

// method 1
#$sql = $wpdb->prepare("UPDATE {$wpdb->users} SET user_login = %s WHERE ID = %d", $user_email, $user_id);
#$wpdb->query($sql);    
// method 2
$wpdb->update($wpdb->users, array('user_login' => $user_email), array('ID' => $user_id));

You can't use %s for table names or they'll get quoted:

"UPDATE 'wp_users' SET user_login='[email protected]' WHERE ID=1" which would not work.