먼저 CONNECT BY 절 이용..

---------------------------------------------------------------------------------------------------------------------------

자연수 : n

SELECT /*+ ORDERED USE_NL(A,B) */ 
                NO1 VAL
FROM ( 
            SELECT DECODE(SIGN(n-LEVEL),-1,(n*2)-LEVEL,LEVEL) NO1
            FROM DUAL
            CONNECT BY LEVEL <= (n*2)-1
            ) A,
           (
           SELECT LEVEL NO2
           FROM DUAL
           CONNECT BY LEVEL <= POWER(n,2)
           ) B
WHERE A.NO1 >= B.NO2;

---------------------------------------------------------------------------------------------------------------------------

COPY_T 테이블 이용

요거 따로 활용 용도는 다들 아실거라..생략

COPY_T 컬럼명이 NO 일때  데이타는 1,2,3.......N 들어있다치고..^^*

---------------------------------------------------------------------------------------------------------------------------

SELECT /*+ ORDERED USE_NL(A, B) */
                DECODE(SIGN(N-A.NO),-1,(N*2)-A.NO,A.NO) VAL
FROM (
            SELECT 3 N -- 자연수
            FROM DUAL
            ) V, COPY_T A, COPY_T B
WHERE A.NO <= (N*2)-1
AND DECODE(SIGN(N-A.NO),-1,N*2-A.NO,A.NO) >= B.NO;

---------------------------------------------------------------------------------------------------------------------------