declare @test table(一级 varchar(1), 二级 varchar(1), 三级 varchar(1))
insert into @test
select 'a', 'b', 'e' union all
select 'a', 'f', '' union all
select 'c', 'd', 'x' union all
select 'c', 'h', ''
;with cte as
(
    select row_number() over(order by 一级) rn,* from @test
)
,t as
(
    select row_number() over(order by rn,级别)id,级别,值 from
    (
        select rn,一级 as 值,1 级别 from cte
        union all
        select rn,二级,2 from cte
        union all
        select rn,三级,3 from cte
    )t
    where 值<>''
)
select 级别,值 from t a
where not exists(select 1 from t where a.id>id and 级别=a.级别 and 值=a.值)
order by id
/*
级别          值
----------- ----
1           a
2           b
3           e
2           f
1           c
2           d
3           x
2           h
*/