WITH T AS (
 SELECT '20180001' AS T1,
            'TEST1' AS T2
     FROM DUAL
     UNION ALL
     SELECT '20180001' AS T1,
            'TEST2' AS T2
     FROM DUAL
     UNION ALL
     SELECT '20180002' AS T1,
            'TEST3' AS T2
     FROM DUAL
     UNION ALL
     SELECT '20180002' AS T1,
            'TEST4' AS T2
     FROM DUAL
)

SELECT B.RN CNT  
     , A.T1 
     , A.T2 
  FROM T A
     , (SELECT ROWNUM RN , T1 
          FROM (SELECT T1 FROM T GROUP BY T1 ORDER BY T1 DESC )
       ) B
  WHERE A.T1 = B.T1    
 ORDER BY A.T1 DESC
  
  

SELECT DENSE_RANK() OVER(ORDER BY t1 DESC) dr
     , t1, t2
  FROM t
;