当前时间：

mysql> select now();

+---------------------+| now()               |+---------------------+| 2014-07-03 21:16:22 |+---------------------+1 row in set (0.00 sec)下一个月：> select date_add(now(),interval 1 month);+----------------------------------+| date_add(now(),interval 1 month) |+----------------------------------+| 2014-08-03 21:16:28              |+----------------------------------+1 row in set (0.00 sec)上一个月：mysql> select date_add(now(),interval -1 month);+-----------------------------------+| date_add(now(),interval -1 month) |+-----------------------------------+| 2014-06-03 21:17:02               |+-----------------------------------+1 row in set (0.00 sec)

三个月前：

DATE_SUB(NOW(), INTERVAL 3 MONTH)

三个天前：

SELECT DATE_SUB(NOW(), INTERVAL 3 DAY)