;with f as
(
select id=row_number()over(partition by a order by getdate()),* from tb
)
select
  isnull(a.a,'') as a,isnull(b.b,'') as b
from
(select px=row_number()over(order by getdate()),* from (select distinct id,a from f where id=1)t)a
left join
 (select px=row_number()over(order by getdate()),* from (select distinct id,b from f where id=1)t)b
on
 a.px=b.px

;with f as
(
select id=row_number()over(partition by a order by getdate()),* from tb   --按照A列排序
)


select
  isnull(a.a,'') as a,isnull(b.b,'') as b  --A列，B列有值的直接列出，没有的就显示为空字符
from
(select px=row_number()over(order by getdate()),* from (select distinct id,a from f where id=1)t)a  --取出按照A列中的序列（不重复的）
left join --俩个序列进行连接
 (select px=row_number()over(order by getdate()),* from (select distinct id,b from f where id=1)t)b  --取出按照B列中的序列（不重复的）
on
 a.px=b.px