[PL\SQL] How to Join on top (First) row

SELECT *
  FROM (SELECT ROWNUM t FROM DUAL CONNECT BY LEVEL < 6)
  JOIN (SELECT v, ROW_NUMBER() OVER(PARTITION BY v ORDER BY 1) rwnm
                     FROM (SELECT 1 v
                              FROM DUAL
                            UNION ALL
                            SELECT 1 FROM DUAL
                            UNION ALL
                            SELECT 2 FROM DUAL)) ON t = v
                                                    AND rwnm = 1;