[DB] [Oracle] Get the last day of the specified month, add/subtract the month based on the current date

Last_day: returns the date of the last day of the month that contains the date parameter.

Select last_day (sysdate) from dual;

Last_day (sysdate)
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2008/02/29 11:24:04
SQL> select last_day (date '2017-02-15 ') from dual;

Last_day (date '2017-
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1892/02/29 00:00:00

 

Add_months: Add/subtract a month based on the current date, and return the plus/minus date.

SQL> select add_months (sysdate,-3) three_months_ago from dual;

Three_months_ago
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2007/11/16 11:23:16