LAST_DAY function returns the last day of the month in which the input date falls in.

The syntax of this function is: LAST_DAY(datetime-expression).

Example:

The Sysdate in this example is: 10/29/2018 8:24:07 PM

SELECT LAST_DAY (SYSDATE) FROM DUAL;

Result: 10/31/2018 8:24:07 PM

Example 2:

The Sysdate in this example is: 10/29/2018 8:24:46 PM

SELECT LAST_DAY (SYSDATE-300) FROM DUAL;

Result: 1/31/2018 8:24:46 PM