create table test1(id number(5),ID_VERSION number(2));
insert into test1 values(1000,1);
insert into test1 values(1000,2);
insert into test1 values(1000,3);
insert into test1 values(1000,4);
insert into test1 values(1000,5);
insert into test1 values(2000,5);


create table test2(id number(5),ID_NUM number(2));
insert into test2 values(1000,3);
insert into test2 values(1000,4);
insert into test2 values(2000,4);
insert into test2 values(2000,5);

select case when a.id is null then b.id else a.id end id,
       a.id_version,b.id_num 
from test1 a full join test2 b on a.id=b.id and a.id_version=b.id_num
order by a.id,a.id_version


       id   ID_VERSION id_num 
-----------------------------------------
1    1000    1    
2    1000    2    
3    1000    3    3
4    1000    4    4
5    1000    5    
6    2000    5    5
7    2000        4