MySql日期相关

select DATE_FORMAT( now(), '%Y%m%d')
select DATE(now())

select YEAR(DATE_SUB(NOW(),INTERVAL 1 YEAR))

select date_add(now(),interval '2' day);  #后2天
select date_add(now(),interval '2' hour);
select date_add(now(),interval '2' minute);
select date_add(now(),interval '2' second);
select date_add(now(),interval '2' week);
select date_add(now(),interval '2' month);
select date_add(now(),interval '2' quarter); #季度
select date_add(now(),interval '2' year);
select date_add(now(),interval '2:10:40' hour_second); #可以一次性从时分秒分别变化
select date_add(now(),interval '-2:10:40' hour_second); #可以一次性从时分秒分别变化，负号表示减，过去的时刻

select datediff('2020-02-20', '2020-01-30')#前面的日期减去后面的日期，返回天数
select datediff('2020-02-20', '2020-04-10')#前面的日期减去后面的日期，返回天数
select datediff('2020-02-20 08:20:30', '2020-04-10 10:54:43')s

# timediff
select timediff('12:23:10','10:10:35') diff_time;  #时间差，时分秒，但是该函数的结果有范围限制，只从：从-838:59:59到838:59:59
select timediff('2020-02-02 12:00:00','12:00:00') as diff_time;   #前后格式不一致时，为Null 

select timediff('2020-01-01 00:00:00', '2020-04-01 00:00:00') as diff_hour;  #结果有误，因为超出限制，事实上，3个月的时间，值远比结果大，要得到正确的，可以用：timestampdiff

# 功能最多的方式可以是：timestampdiff
select timestampdiff(hour, '2020-01-01 00:00:00', '2020-04-01 00:00:00') as diff_hour; #返回的是相差的小时
select timestampdiff(day, '2020-01-01 00:00:00', '2020-02-01 00:00:00') as diff_day; #返回的是相差的天数
select timestampdiff(month, '2020-01-01 00:00:00', '2020-02-01 00:00:00') as diff_month; #返回的是相差的月份
select timestampdiff(year, '2020-01-01 00:00:00', '2020-02-01 00:00:00') as diff_year; #返回的是相差的年份
select timestampdiff(second, '2020-01-01 01:10:10', '2020-01-01 00:00:00') as diff_second; #返回的是相差的秒数
select timestampdiff(minute, '2020-01-01 01:10:10', '2020-01-01 00:00:00') as diff_minute; #返回的是相差的分钟