asp问题,有关ADO中查询语句

[jianchengfine]

我要实现从一个数据库的多个表查询同一个字段(数字型的),然后选择头10个,
如何写呢?
select top 10 a.hit,b.hit from a,b order by a.hit and b.hit desc

select top 10 a.hit,b.hit from a,b order by hit desc
用了,都不行,怎么不行呢?

[kevin_gao]

select top 10 hit from
(
select distinct a.hit as hit from a
union
select distinct b.hit as hit from b
) as pp

[kevin_gao]

select top 10 hit from
(
select distinct a.hit as hit from a
union
select distinct b.hit as hit from b
) as pp order by hit desc