gistfile1.sql

select personas_23_dic.updated_at as OLD, personas.updated_at as NEW
from personas_23_dic
join personas
where personas_23_dic.id = personas.id
and DATE(personas.updated_at) = '2013-12-24'
order by personas.updated_at asc

// UPDATE

UPDATE personas NUEVA
left join personas_23_dic VIEJA ON
	NUEVA.id = VIEJA.id
set 
	updated_at = if(DATE(personas.updated_at) = '2013-12-24', personas_23_dic.updated_at, personas.updated_at)