declare @rowid int set @rowid=2

select * from 
(
select * from a
union all
select * from b
) aa where rowid=2 order by 排序列

------解决方案--------------------

SQL code

-----------sql中没有rowid，oracle中才有的。
-----------sql中的行号是，row_number
select * from (select rowid=row_number() over(order by xh),* from(
select * from goal
union all
select * from goal )tmp)tmp2 where rowid=1