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SQL> SELECT
  2     LEVEL Month,
...
        12 31

12 rows selected.

SELECT
    TO_CHAR(ADD_MONTHS(TO_DATE('1', 'DDD'), LEVEL) - 1, 'DD')
...
    Dual
CONNECT BY
    LEVEL < 13;

SELECT
    TO_CHAR(ADD_MONTHS(DATE '2014-1-1', LEVEL) - 1, 'DD')
...
    Dual
CONNECT BY
    LEVEL < 13;

SELECT TO_CHAR(LAST_DAY(TO_DATE(LEVEL,'MM')),'DD')FROM Dual CONNECT BY
+ LEVEL<13;