2개의 쿼리는 동일 테이블과 동일 조건입니다.

단 하나는 UNION ALL 로 가져오고 하나는 풀아우터 조인 방식으로 가져 왔습니다.

데이터가 몃개 없어서 결과는 동일한대 혹시 결과가 다르게 나올수도 있을가요?

   WHERE A.PJT = 'ZRE'    AND TYPE = 'P' 이조건으로 데이터는 여러건 나옵니다.

SELECT RN, CLASS, MAX(C1) AS C1 , MAX(C2) AS C2 ,MAX(C3) AS C3, MAX(C4) AS C4 , MAX(C5) AS C5 , MAX(C6) AS C6 , MAX(C4) AS C7 , MAX(C5) AS C8 , MAX(C6) AS C9
FROM (
       SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
            , FROM_S AS c1 , TO_S AS c2, DESCRT AS c3 , '' AS c4 , '' AS c5, '' AS c6 , '' AS c7 , '' AS c8, '' AS c9
           FROM EMPT A
           WHERE A.PJT = 'ZRE'        
           AND TYPE = 'P'
       
       UNION ALL  
       
        SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
            , '' AS c1 , '' AS c2, '' AS c3 , FROM_S AS c4 , TO_S AS c5, DESCRT AS c6   , '' AS c7 , '' AS c8, '' AS c9
           FROM EMPT A
           WHERE A.PJT = 'ZRE'        
           AND TYPE = 'F'
           
             UNION ALL   
             
        SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
            , '' AS c1 , '' AS c2, '' AS c3 ,  '' AS c4 , '' AS c5, '' AS c6 , FROM_S AS c7 , TO_S AS c8, DESCRT AS c9
           FROM EMPT A
           WHERE A.PJT = 'ZRE'       
           AND TYPE = 'B'
    
    )
    GROUP BY CLASS, RN  
    ORDER BY CLASS  , RN
    
/////////////////////////////////

WITH
DTL AS (
    SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
        , FROM_S AS c1 , TO_S AS c2, DESCRT AS c3 
    FROM EMPT A
    WHERE A.PJT = 'ZRE'  
    AND TYPE = 'P'
)
,
ING AS (
 SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
       ,  FROM_S AS c1 , TO_S AS c2, DESCRT AS c3 
    FROM EMPT A
    WHERE A.PJT = 'ZRE'   
    AND TYPE = 'F'
)
,
VB AS (
   SELECT ROW_NUMBER() OVER (PARTITION BY CLASS ORDER BY CLASS DESC) AS RN , CLASS
       ,  FROM_S AS c1 , TO_S AS c2, DESCRT AS c3 
      FROM EMPT A
      WHERE A.PJT = 'ZRE'   
      AND TYPE = 'B'
)
SELECT A.RN, A.CLASS, A.C1, A.C2, A.C3 , B.C1, B.C2, B.C3 ,  C.C1, C.C2, C.C3
 FROM DTL           A
FULL OUTER JOIN ING B ON A.RN = B.RN  AND A.CLASS = B.CLASS 
FULL OUTER JOIN VB  C ON COALESCE(A.RN, B.RN) = C.RN  AND COALESCE(A.CLASS, B.CLASS) = C.CLASS 
ORDER BY A.CLASS , RN