在mysql中得到两个表的混合 - Get out a mix from both tables in mysql

我如何从mysql ORDER BY日期从两个表限制4 ?我想从两个表中得到一个混合ORDER BY date>= date (NOW()).

tbl1 
id      place1    date1  
1   |  example | 2013-01-05
2   |  example | 2013-07-05
3   |  example | 2013-23-05
tbl2
id      place2    date2  
1   |  example | 2013-05-05
2   |  example | 2013-06-05
3   |  example | 2013-20-05

SELECT *
FROM (SELECT id, place1 place, date1 date
        FROM tbl1
       WHERE date1 > CURDATE()
      UNION
      SELECT id, place2 place, date2 date
        FROM tbl2
       WHERE date2 > CURDATE()) tbl12
ORDER BY date DESC
LIMIT 4