YYYY, MM 2개를 정렬 조건으로 넣고 2번째 것을 조회되게 하였습니다.

WITH T1 AS
(
SELECT '1' AS CODE, '2013' AS YYYY, '01' AS MM FROM DUAL UNION ALL
SELECT '2' AS CODE, '2013' AS YYYY, '02' AS MM FROM DUAL UNION ALL
SELECT '3' AS CODE, '2013' AS YYYY, '03' AS MM FROM DUAL UNION ALL
SELECT '4' AS CODE, '2013' AS YYYY, '04' AS MM FROM DUAL UNION ALL
SELECT '5' AS CODE, '2013' AS YYYY, '05' AS MM FROM DUAL UNION ALL
SELECT '6' AS CODE, '2014' AS YYYY, '02' AS MM FROM DUAL
)
SELECT * FROM (
        SELECT CODE
                    , YYYY
                    , MM
                    , ROW_NUMBER() OVER (ORDER BY YYYY DESC, MM DESC) AS RN
        FROM T1
) WHERE RN = 2 ;

이번달 이전에 대한 조건까지 넣으시려면 WHERE 조건이 추가됩니다.

 WITH T1 AS
(
SELECT '1' AS CODE, '2013' AS YYYY, '01' AS MM FROM DUAL UNION ALL
SELECT '2' AS CODE, '2013' AS YYYY, '02' AS MM FROM DUAL UNION ALL
SELECT '3' AS CODE, '2013' AS YYYY, '03' AS MM FROM DUAL UNION ALL
SELECT '4' AS CODE, '2013' AS YYYY, '04' AS MM FROM DUAL UNION ALL
SELECT '5' AS CODE, '2013' AS YYYY, '05' AS MM FROM DUAL UNION ALL
SELECT '6' AS CODE, '2014' AS YYYY, '02' AS MM FROM DUAL
)
SELECT * FROM (
        SELECT CODE
                    , YYYY
                    , MM
                    , ROW_NUMBER() OVER (ORDER BY YYYY DESC, MM DESC) AS RN
        FROM T1
        WHERE YYYY||MM <= TO_CHAR(SYSDATE, 'YYYYMM')
) WHERE RN = 2 ;