create table #t1(mesid int)
insert #t1
select 10 union all
select 9

create table #t2(mesid int)
insert #t2
select 9 union all
select 8 union all
select 7

select id=identity(int,1,1),mesid into #t3 from
(
select mesid from #t1
union all
select mesid from #t2
) as a

select mesid from #t3 a where id=(select min(id) from #t3 where mesid=a.mesid) order by id
/*
10
9
8
7
*/

drop table #t1,#t2,#t3