orclx> with d10 as (select * from emp where deptno=10),
  2  d20 as (Select * from emp where deptno=20)
  3  select * from d10
  4  union all
  5  select * from d20;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
      7782 CLARK      MANAGER         7839 1981-06-09:00:00:00       2450                    10
      7839 KING       PRESIDENT            1981-11-17:00:00:00       5000                    10
      7934 MILLER     CLERK           7782 1982-01-23:00:00:00       1300                    10
      7369 SMITH      CLERK           7902 1980-12-17:00:00:00        800                    20
      7566 JONES      MANAGER         7839 1981-04-02:00:00:00       2975                    20
      7788 SCOTT      ANALYST         7566 1987-04-19:00:00:00       3000                    20
      7876 ADAMS      CLERK           7788 1987-05-23:00:00:00       1100                    20
      7902 FORD       ANALYST         7566 1981-12-03:00:00:00       3000                    20

8 rows selected.

orclx>