SELECT MIN(HIREDATE), MAX(HIREDATE)
FROM EMP;

SELECT a.*, a.hiredate FROM EMP a
INNER JOIN
(SELECT hiredate, MIN(HIREDATE), MAX(HIREDATE)
FROM EMP group by hiredate) b
ON a.HIREDATE=b.HIREDATE;

SQL> with t as (
  2             select  e.*,
  3                     dense_rank() over(order by hiredate nulls last) drnk,
  4                     dense_rank() over(order by hiredate desc nulls last) rdrnk
  5               from emp e
  6            )
  7  select  *
  8    from  t
  9    where drnk = 1
 10       or rdrnk = 1
 11  /

     EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM     DEPTNO       DRNK      RDRNK
---------- ---------- --------- ---------- --------- ---------- ---------- ---------- ---------- ----------
      7876 ADAMS      CLERK           7788 23-MAY-87       1100                    20         13       1
      7369 SMITH      CLERK           7902 17-DEC-80        800                    20          1      13

SQL>

SELECT A.* , ' earliest hire date emp' FROM emp A WHERE hiredate IN 
((SELECT MIN(hiredate) FROM emp),(SELECT MAX(hiredate) FROM emp));
SELECT A.* , ' earliest hire date emp' FROM emp A WHERE hiredate IN (SELECT 
MIN(hiredate) FROM emp)
UNION ALL
SELECT A.*, 'latest hire date emp' FROM emp A WHERE hiredate IN (SELECT 
MAX(hiredate) FROM emp);

Select a.* , ' earliest hire date emp' from emp a where hiredate in (select 
min(hiredate) from emp Union Select max(hiredate) from emp);