추가여부 컬럼을 넣는 방법이 어떻까요?
그래야 하드코딩 하지 않고 좋을거 같네요.
이미 운영중이라면.. 하드코딩 ^^
좋은 하루 되세요.

WITH T (NUM, VALUE, NEW_YN) AS
 ( SELECT 1, 3 , 'N' FROM DUAL UNION ALL
 SELECT 3, 2 , 'N' FROM DUAL UNION ALL
 SELECT 8, 5.9 , 'N' FROM DUAL UNION ALL
 SELECT 10, 11 , 'Y' FROM DUAL UNION ALL
 SELECT 11, 2 , 'N' FROM DUAL UNION ALL
 SELECT 17, 2 , 'N' FROM DUAL
 )
SELECT A.*
 FROM (
 SELECT T.*
 , LAG(VALUE) OVER(ORDER BY NUM) AS BEF_VALUE --이전자료
 , LEAD(VALUE) OVER(ORDER BY NUM) AS AFT_VALUE --이후자료
 FROM T
 ) A
 WHERE A.NEW_YN = 'Y'
 AND A.BEF_VALUE = 5.9 ;