SELECT dede_archives.id AS id, dede_archives.title, dede_addonarticle.body
FROM dede_archives,dede_addonarticle
where dede_archives.id = dede_addonarticle.aid AND body LIKE '%string%'

UPDATE dede_addonarticle
SET body = REPLACE(body,"old_string","new_string")
WHERE dede_addonarticle.body LIKE '%old_string%'