SELECT * FROM 
(SELECT EMP.*, ROW_NUMBER() OVER (ORDER BY EMPNO)AS RNO FROM EMP 
WHERE ROWNUM <= (SELECT COUNT(*)/2 FROM EMP))
WHERE RNO=(SELECT COUNT(*)/2 FROM EMP);

EMPNO   ENAME   JOB     MGR     HIREDATE                SAL     COMM   DEPTNO  RNO
7782	CLARK	MANAGER	7839	09-JUN-1981 00:00:00	2450		10	7

SELECT * FROM 
(SELECT EMP.*, ROW_NUMBER() OVER (ORDER BY EMPNO)AS RNO FROM EMP) 
WHERE RNO=(SELECT ceil(COUNT(*)/2) FROM EMP);

SELECT *
  FROM (SELECT Emp.*,
               ROW_NUMBER () OVER (ORDER BY Empno) AS Rno, 
               count(*) over () tot_recs 
          FROM Emp)
where rno = ceil(tot_recs/2);

orclz>
orclz> select * from emp order by empno offset (select count(*)/2 -1 from emp) rows fetch next 1 row only;

     EMPNO ENAME      JOB              MGR HIREDATE                   SAL       COMM     DEPTNO
---------- ---------- --------- ---------- ------------------- ---------- ---------- ----------
      7782 CLARK      MANAGER         7839 1981-06-09:00:00:00       2450                    10


Execution Plan
----------------------------------------------------------
Plan hash value: 532028908

---------------------------------------------------------------------------------
| Id  | Operation              | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |        |    14 |  1582 |     8  (13)| 00:00:01 |
|*  1 |  VIEW                  |        |    14 |  1582 |     4  (25)| 00:00:01 |
|   2 |   WINDOW SORT          |        |    14 |  1218 |     4  (25)| 00:00:01 |
|   3 |    TABLE ACCESS FULL   | EMP    |    14 |  1218 |     3   (0)| 00:00:01 |
|   4 |   SORT AGGREGATE       |        |     1 |       |            |          |
|   5 |    INDEX FAST FULL SCAN| PK_EMP |    14 |       |     2   (0)| 00:00:01 |
---------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("from$_subquery$_002"."rowlimit_$$_rownumber"<=CASE  WHEN
              ( (SELECT COUNT(*)/2-1 FROM "EMP" "EMP")>=0) THEN
              FLOOR(TO_NUMBER(TO_CHAR( (SELECT COUNT(*)/2-1 FROM "EMP" "EMP")))) ELSE
              0 END +1 AND "from$_subquery$_002"."rowlimit_$$_rownumber"> (SELECT
              COUNT(*)/2-1 FROM "EMP" "EMP"))

Note
-----
   - dynamic statistics used: dynamic sampling (level=2)

orclz>

select * from emp order by empno offset (select count(*)/2 -1 from emp) rows fetch next row only;