1. 时间差函数（TIMESTAMPDIFF、DATEDIFF）

需要用MySQL计算时间差，使用TIMESTAMPDIFF、DATEDIFF，记录一下实验结果

--0select datediff(now(), now());--2select datediff('2015-04-22 23:59:00', '2015-04-20 00:00:00');--2select datediff('2015-04-22 00:00:00', '2015-04-20 23:59:00');--1select TIMESTAMPDIFF(DAY, '2015-04-20 23:59:00', '2015-04-22 00:00:00');--2select TIMESTAMPDIFF(DAY, '2015-04-20 00:00:00', '2015-04-22 00:00:00');--2select TIMESTAMPDIFF(DAY, '2015-04-20 00:00:00', '2015-04-22 12:00:00');--2select TIMESTAMPDIFF(DAY, '2015-04-20 00:00:00', '2015-04-22 23:59:00');--71select TIMESTAMPDIFF(HOUR, '2015-04-20 00:00:00', '2015-04-22 23:00:00');--4260select TIMESTAMPDIFF(MINUTE, '2015-04-20 00:00:00', '2015-04-22 23:00:00');

关于TIMESTAMPDIFF描述，见http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_timestampdiff

如需知道TIMESTAMPDIFF还能以哪些单位返回数据，可参考TIMESTAMPADD的描述：http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html#function_timestampadd

2. 日期转换计算函数（date_add、day、date_format、str_to_date）

-- 用日期与字符串转换，计算当月第一天、下月第一天select curdate() as '当前日期', DATE_FORMAT(curdate(), '%Y-%m') as '当前月份', str_to_date(concat(DATE_FORMAT(curdate(), '%Y-%m'), '-01'), '%Y-%m-%d') as '当前月的第一天', date_add(str_to_date(concat(DATE_FORMAT(curdate(), '%Y-%m'), '-01'), '%Y-%m-%d'), interval 1 month) as '下月的第一天';-- 当前月的最后一天select last_day(curdate());-- 下月第一天select date_add(last_day(curdate()), interval 1 day);-- 当天为当月的第几天select day(curdate());-- 当月第一天select date_add(curdate(), interval 1-(day(curdate())) day);

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