Elgg: Delete entity rows where the associated secondary table rows no longer exist

elgg_prune_entities.sql

DELETE FROM elgg_entities
WHERE guid in ( 
  SELECT * FROM (
    SELECT e.guid FROM elgg_entities AS e
    LEFT JOIN elgg_users_entity AS u ON (e.guid = u.guid)
    WHERE e.type = 'user'
    AND u.guid IS NULL
  ) AS q1
  UNION
  SELECT * FROM (
    SELECT e.guid FROM elgg_entities AS e
    LEFT JOIN elgg_objects_entity AS o ON (e.guid = o.guid)
    WHERE e.type = 'object'
    AND o.guid IS NULL
  ) AS q2
)