How to Delete Orphaned Post Meta Data in WordPress

<?php

// Warning! Please create a backup of your database before running this snippet
// This snippet should only be ran in "Manual" mode.

global $wpdb;

$affected_rows = $wpdb->query("DELETE postmeta FROM {$wpdb->postmeta} postmeta LEFT JOIN {$wpdb->posts} posts ON posts.ID = postmeta.post_id WHERE posts.ID IS NULL");

echo "Deleted $affected_rows orphaned meta entries.";