(SELECT id, first_name,last_name,email,birthdate,
 DATE_FORMAT(added,"%d %m %Y") as added,
 DATE_FORMAT(added,"%H %i") as added_time,
 DATE_FORMAT(added,"%W") as week_day,
 DATE_ADD(birthdate, INTERVAL 18 year)as urodziny FROM authors ORDER BY `birthdate` LIMIT 5)
UNION
(SELECT id, first_name,last_name,email,birthdate,
 DATE_FORMAT(added,"%d %m %Y") as added,
 DATE_FORMAT(added,"%H %i") as added_time,
 DATE_FORMAT(added,"%W") as week_day,
 DATE_ADD(birthdate, INTERVAL 18 year) From  authors)ORDER BY `birthdate` ASC limit 10