MySQL ADDDATE of function tutorial

ADDDATE(date,INTERVAL expr unit), ADDDATE(expr,days)

ADDDATE() is a synonym for DATE_ADD() when the second argument is called in the interval form. The related function SUBDATE() is a pronoun for DATE_SUB(). For more information on the cell parameters on the interval, see the description of DATE_ADD().

mysql> SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY);
+---------------------------------------------------------+
| DATE_ADD('1998-01-02', INTERVAL 31 DAY)         |
+---------------------------------------------------------+
| 1998-02-02                       |
+---------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY);
+---------------------------------------------------------+
| ADDDATE('1998-01-02', INTERVAL 31 DAY)         |
+---------------------------------------------------------+
| 1998-02-02                       |
+---------------------------------------------------------+
1 row in set (0.00 sec)

When called in the form of the second argument, MySQL adds it to expr as an integer number of days.

mysql> SELECT ADDDATE('1998-01-02', 31);
+---------------------------------------------------------+
| DATE_ADD('1998-01-02', INTERVAL 31 DAY)         |
+---------------------------------------------------------+
| 1998-02-02                       |
+---------------------------------------------------------+
1 row in set (0.00 sec)