MySQL中ADDDATE()函数的使用教程

adddate(date,interval expr unit), adddate(expr,days)

当被调用的第二个参数的区间形式，adddate()是date_add()的同义词。相关功能subdate()是date_sub()的代名词。对于区间上的单元参数的详细信息，请参阅date_add()的说明。

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)

当被调用的第二个参数的形式，mysql的把它作为一个整数天数添加到expr。

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)