select * from (select no, 국가, 날씨, 날짜 rank() over(partition by 국가  order by 날짜 desc)  rn from t)

where rn = 1

WITH T1 as
(
  SELECT '1' RN, '한국' COUNTRY, '맑음' WEATHER, '2019.07.17' IL FROM DUAL
    UNION ALL
  SELECT '2' RN, '한국' COUNTRY, '맑음' WEATHER, '2019.07.19' IL FROM DUAL
    UNION ALL
  SELECT '3' RN, '미국' COUNTRY, '비' WEATHER, '2019.07.11' IL FROM DUAL
    UNION ALL
  SELECT '4' RN, '호주' COUNTRY, '안개' WEATHER, '2019.07.10' IL FROM DUAL
)
-- 1) 동일한 국가 날씨 중에서
-- 2) 마지막 업데이트 된 정보만 표기 
-- 3) 정렬 조건이 없네요!
 SELECT * 
   FROM (
        SELECT Row_Number() OVER(PARTITION BY COUNTRY ORDER BY IL) RN
              ,COUNTRY
              ,WEATHER
              ,IL
          FROM T1
        )
  WHERE RN=1
  ORDER BY IL DESC;