Używanie fikcyjnych kolumn do uwzględnienia różnych struktur, unii, aby do nich dołączyć, a rodzica wybierz do obsługi kolejności:
SELECT * FROM (
(SELECT foo.id, NULL AS title, NULL AS body, foo.downloads, foo.views, foo.created FROM foo)
UNION ALL
(SELECT NULL AS id, bar.title, bar.body, NULL AS downloads, NULL AS views, bar.created FROM bar)
) results
ORDER BY created ASC