select last_day( sysdate ) "Last day of this month"

  
SQL>
SQL> select last_day( sysdate ) "Last day of this month"
  2  from dual;
Last day
---------
30-JUN-08

1 row selected.

SQL>
SQL> --

1.	LAST_DAY: Get the last day of each month
2.	Simple demo for LAST_DAY function
3.	Finding the last day of the month starting summer
4.	Calculating the Number of Days of Summer in June
5.	select last_day( date'2000-02-01' ) "Leap Yr?"
6.	LAST_DAY(hire_date)+1
7.	LAST_DAY(x): get the date of the last day of the month that contains x.

select last_day( sysdate ) "Last day of this month" : LAST_DAY « Date Timezone « Oracle PL / SQL