아래SQL문장 출력결과
2623   Y   2019.09.25   B,  Y
2623   B   2019.09.26   B,  B
2623   B   2019.09.27   B,  B
----
제각 생각했던 출력결과
2623   Y   2019.09.25   B,  B
2623   B   2019.09.26   B,  B
2623   B   2019.09.27   B,  B

이유>  일자를 DESC 후 FIRST_VALUE()
            일자를 ASC 후 LAST_VALUE() 
           위와 같은 기준이기에 ..값은 값이 나올거라 예상했는데.. 왜 다르게 나올까요?


WITH V_VB AS
   ( SELECT '2623' AS RSTR_CD, 'B' SIGNL_LIGHT, '20190927' AS REGI_DTIME FROM DUAL UNION ALL
     SELECT '2623' AS RSTR_CD, 'B' SIGNL_LIGHT, '20190926' AS REGI_DTIME FROM DUAL UNION ALL
     SELECT '2623' AS RSTR_CD, 'Y' SIGNL_LIGHT, '20190925' AS REGI_DTIME FROM DUAL
   )
SELECT VB.*
     , FIRST_VALUE(VB.SIGNL_LIGHT) OVER (PARTITION BY VB.RSTR_CD ORDER BY VB.REGI_DTIME DESC) AS FIST_SIGNL_LIGHT
     , LAST_VALUE(VB.SIGNL_LIGHT) OVER  (PARTITION BY VB.RSTR_CD ORDER BY VB.REGI_DTIME ASC)  AS LAST_SIGNL_LIGHT
  FROM V_VB VB;