SELECT lvl num, TO_CHAR (MAX (FIRST), 'MONTH') FIRST, TO_CHAR (MAX (second), 'MONTH') second
    FROM (    SELECT LEVEL lvl, ADD_MONTHS (TRUNC (SYSDATE), LEVEL - 1) FIRST, NULL second
                FROM DUAL
          CONNECT BY LEVEL <= 6
          UNION ALL
              SELECT LEVEL lvl, NULL, ADD_MONTHS (TRUNC (SYSDATE), LEVEL + 5)
                FROM DUAL
          CONNECT BY LEVEL <= 6)
GROUP BY lvl
ORDER BY lvl