SQL> SELECT
  2     LEVEL Month,
  3     TO_CHAR(LAST_DAY(TO_DATE(LEVEL  || '/1/' ||
  4     TO_CHAR(SYSDATE, 'YYYY'), 'MM/DD/YYYY')),'DD') Days
  5  FROM
  6     Dual
  7  CONNECT BY
  8     LEVEL <= 12;

     MONTH DA
---------- --
         1 31
         2 28
         3 31
         4 30
         5 31
         6 30
         7 31
         8 31
         9 30
        10 31
        11 30
        12 31

12 rows selected.


##</code><code>##

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


##</code><code>##

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


##</code><code>##

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