如何在一主表和两从表中,统计最后的登记日期

[lbd8848]

表a
uid uname
------------------
001 aaaaa
002 bbbbb
003 ccccc
004 ddddd

表b
uid adddate .....
------------------------
002 2005-09-12 06:12:02
003 2005-09-11 04:09:21
002 2005-09-11 09:09:21
001 2005-09-21 21:21:21
001 2005-09-21 11:11:11
002 2005-09-13 12:09:07

表c
uid adddate ......
-----------------------------
001 2005-09-22 00:09:00
003 2005-08-28 01:01:00
001 2005-09-01 12:02:11

从三表中取出如下的结果
uid uname addate
-----------------------------
001 aaaaa 2005-09-22 00:09:00
002 bbbbb 2005-09-13 12:09:07
003 ccccc 2005-09-11 04:09:21
004 ddddd null
也即取出表A中所有对应uid最后的登记日期

[伍子V5]

select a.uid,a.uname,bb.addate
from a
left join(select uid,max(addate) addate from (select * from b union select * from c)aa group by aa.uid)bb
where a.uid=bb.uid