칼럼명은 제가 임의로 수정한 부분이 있어요

HQ_CODE를 HQ_CD로

테이블명을 AA,BB로 .. 수정해서 실행해 보세요 ^^

SELECT HQ_CD,

         DECODE(A,1,
             (SELECT MAX(b.BASIC_SEQ) FROM BB b

                 WHERE b.ANSWER_GRADE = 'Y' AND b.HQ_CD = a.HQ_CD),
             (SELECT MAX(b.BASIC_SEQ) FROM BB b

                 WHERE b.ANSWER_GRADE = 'N' AND b.HQ_CD = a.HQ_CD)) B
FROM (
 SELECT HQ_CD,
        SIGN(SUM(DECODE(ANSWER_GRADE,'Y',1,0))) A
   FROM AA
 WHERE ANSWER_GRADE IS NOT NULL
GROUP BY HQ_CD
) A;