The LAST_DAY function returns the last day of the month in which a particular date falls.
Example 8-5 Calculating Remaining Days in a Month
The following statement calculates how many days remain between today's date and the end of the month.
SHOW JOINCHARS('Days left: ' LAST_DAY(SYSDATE) - SYSDATE)
When today's date is September 8, 2000, then this statement returns the following.
Days left: 22