Delete orphaned post meta data

This snippet will delete all the metadata that doesn’t belong to any post.

<?php
2
3// Warning! Please create a backup of your database before running this snippet
4// This snippet should only be ran in "Manual" mode.
5
6global $wpdb;
7
8$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");
9
10echo "Deleted $affected_rows orphaned meta entries.";