select top 1 userid
from A inner join B on A.userid=B.userid
where sex=1
order by rank
union all
select top 1 userid
from A inner join B on A.userid=B.userid
where sex=2
order by rank

------解决方案--------------------


select userid from b
(
 select sex,min(rank) as rank from  
 (
 select * from a , b
 where a.userid=b.userid
 ) c
 group by sex
) d
where b.rank =d.rank