create table A(no int, data varchar(10))
insert A select 1, 'a'
union all select 2, 'b'
union all select 3, 'c'
create table B(no int, data varchar(10), flag int)
insert B select 4, 'd', 1
union all select 5, 'e', 1
select no, data, flag=null into C from A
union all
select no, data, flag from B
select * from C
--result
no data flag
----------- ---------- -----------
1 a NULL
2 b NULL
3 c NULL
4 d 1
5 e 1