mysql的日期函數. 例子中當前日期：
curdate() 是2013年6月24日。
YEAR() ：顯示年
mysql> select year(curdate()); +-----------------+ | year(curdate()) | +-----------------+ | 2013 | +-----------------+ 1 row in set (0.01 sec)
MONTH() ：顯示月
mysql> select month(curdate()); +------------------+ | month(curdate()) | +------------------+ | 6 | +------------------+ 1 row in set (0.00 sec)
DAYOFMONTH()：顯示日期
mysql> select dayofmonth(curdate()); +-----------------------+ | dayofmonth(curdate()) | +-----------------------+ | 24 | +-----------------------+ 1 row in set (0.08 sec)
