/* Deleting Orphan Postmeta */
DELETE pm
FROM wp_postmeta pm
LEFT JOIN wp_posts wp ON wp.ID = pm.post_id
WHERE wp.ID IS NULL
/* Deleting Orphan Taxonomy Relationships */
DELETE tr FROM wp_term_relationships tr
INNER JOIN wp_term_taxonomy tt ON (tr.term_taxonomy_id = tt.term_taxonomy_id)
WHERE tr.object_id NOT IN (SELECT ID FROM wp_posts);