一、获取当前时间
1.current_date获取当前日期
2018-04-09
 
2.current_timestamp/now()获取当前时间
2018-04-09 15:20:49.247
 
3.时间戳转换字符串格式 
from_unixtime(cloumn,‘yyyy-MM-dd HH:mm:ss‘)
 
二、从日期时间中提取字段 
1.year,month,day/dayofmonth,hour,minute,second
Examples:> SELECT day(‘2009-07-30‘); 30
 
2.dayofweek (1 = Sunday, 2 = Monday, ..., 7 = Saturday),dayofyear
Examples:> SELECT dayofweek(‘2009-07-30‘);　　 5
 
Since: 2.3.0
 
3.weekofyear
weekofyear(date) - Returns the week of the year of the given date. A week is considered to start on a Monday and week 1 is the first week with >3 days.
 
Examples:> SELECT weekofyear(‘2008-02-20‘);　　 8
 
4.trunc截取某部分的日期，其他部分默认为01
第二个参数 ["year", "yyyy", "yy", "mon", "month", "mm"]
 
Examples:
 
> SELECT trunc(‘2009-02-12‘, ‘MM‘);
 2009-02-01
> SELECT trunc(‘2015-10-27‘, ‘YEAR‘);
 2015-01-01
5.date_trunc ["YEAR", "YYYY", "YY", "MON", "MONTH", "MM", "DAY", "DD", "HOUR", "MINUTE", "SECOND", "WEEK", "QUARTER"]
Examples:> SELECT date_trunc(‘2015-03-05T09:32:05.359‘, ‘HOUR‘);　　2015-03-05T09:00:00
 
Since: 2.3.0
 
6.date_format将时间转化为某种格式的字符串
Examples:> SELECT date_format(‘2016-04-08‘, ‘y‘);　　　　2016
 
三、日期时间转换
1.unix_timestamp返回当前时间的unix时间戳
Examples:
 
> SELECT unix_timestamp();　　1476884637
> SELECT unix_timestamp(‘2016-04-08‘, ‘yyyy-MM-dd‘);　　 1460041200
2.from_unixtime将时间戳换算成当前时间，to_unix_timestamp将时间转化为时间戳
Examples:
 
> SELECT from_unixtime(0, ‘yyyy-MM-dd HH:mm:ss‘);　　1970-01-01 00:00:00
>SELECT to_unix_timestamp(‘2016-04-08‘, ‘yyyy-MM-dd‘);　　1460041200
3.to_date/date将字符串转化为日期格式，to_timestamp（Since: 2.2.0）
> SELECT to_date(‘2009-07-30 04:17:52‘);　　2009-07-30
> SELECT to_date(‘2016-12-31‘, ‘yyyy-MM-dd‘);　　 2016-12-31
> SELECT to_timestamp(‘2016-12-31 00:12:00‘);　　 2016-12-31 00:12:00
4.quarter 将1年4等分(range 1 to 4)
Examples:> SELECT quarter(‘2016-08-31‘);  3
 
四、日期、时间计算
1.months_between两个日期之间的月数
months_between(timestamp1, timestamp2) - Returns number of months between timestamp1 and timestamp2.
 
Examples:> SELECT months_between(‘1997-02-28 10:30:00‘, ‘1996-10-30‘);　　3.94959677
 
2. add_months返回日期后n个月后的日期
Examples:> SELECT add_months(‘2016-08-31‘, 1);　　2016-09-30
 
3.last_day(date),next_day(start_date, day_of_week)
Examples:
 
> SELECT last_day(‘2009-01-12‘);　　2009-01-31
> SELECT next_day(‘2015-01-14‘, ‘TU‘);　　2015-01-20
4.date_add,date_sub(减)
date_add(start_date, num_days) - Returns the date that is num_days after start_date.
 
Examples:
 
> SELECT date_add(‘2016-07-30‘, 1);　　2016-07-31
5.datediff（两个日期间的天数）
datediff(endDate, startDate) - Returns the number of days from startDate to endDate.
 
Examples:> SELECT datediff(‘2009-07-31‘, ‘2009-07-30‘); 1
 
6.关于UTC时间
to_utc_timestamp
to_utc_timestamp(timestamp, timezone) - Given a timestamp like ‘2017-07-14 02:40:00.0‘, interprets it as a time in the given time zone, and renders that time as a timestamp in UTC. For example, ‘GMT+1‘ would yield ‘2017-07-14 01:40:00.0‘.
 
Examples:> SELECT to_utc_timestamp(‘2016-08-31‘, ‘Asia/Seoul‘);　　2016-08-30 15:00:0
 
from_utc_timestamp
from_utc_timestamp(timestamp, timezone) - Given a timestamp like ‘2017-07-14 02:40:00.0‘, interprets it as a time in UTC, and renders that time as a timestamp in the given time zone. For example, ‘GMT+1‘ would yield ‘2017-07-14 03:40:00.0‘.
 
Examples:> SELECT from_utc_timestamp(‘2016-08-31‘, ‘Asia/Seoul‘);　　2016-08-31 09:00:00