Plenty of options
SQL> create table t1 ( x int );
Table created.
SQL>
SQL> create table t2 ( x int );
Table created.
SQL>
SQL>
SQL> insert into t1 values (1);
1 row created.
SQL> insert into t1 values (1);
1 row created.
SQL> insert into t1 values (1);
1 row created.
SQL> insert into t1 values (2);
1 row created.
SQL> insert into t1 values (3);
1 row created.
SQL> insert into t1 values (4);
1 row created.
SQL> insert into t1 values (5);
1 row created.
SQL> insert into t2 values (3);
1 row created.
SQL> insert into t2 values (4);
1 row created.
SQL> insert into t2 values (5);
1 row created.
SQL> insert into t2 values (6);
1 row created.
SQL> insert into t2 values (7);
1 row created.
SQL>
SQL> select x from t1
2 union
3 select x from t2;
X
----------
1
2
3
4
5
6
7
7 rows selected.
SQL>
SQL> select * from t1 full outer join t2
2 on ( t1.x = t2.x)
3 where t1.x is not null or
4 ( t1.x is null and t2.x is not null );
X X
---------- ----------
1
1
1
2
3 3
4 4
5 5
6
7
9 rows selected.
SQL>
SQL> select * from t1
2 union all
3 select * from t2 where x not in ( select x from t1 ) ;
X
----------
1
1
1
2
3
4
5
6
7
9 rows selected.
SQL>