mysql计算时间差

SELECT TIMESTAMPDIFF(SECOND, now(), "2012-11-11 00:00:00")
语法为：TIMESTAMPDIFF(unit,datetime1,datetime2)，
其中unit单位有如下几种，分别是：FRAC_SECOND (microseconds), SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR。