postgresql支持的时间类型如下图所示：
日期 date:
建议日期的输入格式为1997-01-01，虽然也支持19970101,1/1/1997,Jan-1-1997等多种格式。
时间戳 timestamp[(p)] with(without) time zone:
其实配置文件是可以设置时区的，且做上层业务时也不会在多个时区间切换，所以一般使用无时区的时间戳就可以满足需要了。
建议时间戳的输入格式为1997-01-01 00:00:00
时间 time[(p)] with(without) time zone:
同样无时区的时间也是可以满足需要的，只表示一天的时间点，不包含日期，可以有如下格式：
12:00:00,120000,12:00
8:00 AM,8:00 PM
时间间隔 interval [fields][(p)]
我还是比较喜欢明确的时间间隔表示方法，如：
1 year 2 months 3 days 4 hours 5 minutes 6 seconds
可以用单词复数，也可以不用
test=# select interval '1 year 2 months 3 days 4 hours 5 minutes 6 seconds'; interval -------------------------------
1 year 2 mons 3 days 04:05:06 (1 row) test=# select interval '2 year 2 months 3 days 4 hours 5 minutes 6 seconds'; interval --------------------------------
2 years 2 mons 3 days 04:05:06 (1 row) test=# select interval '2 year 2 month 3 day 4 hour 5 minute 6 second'; interval --------------------------------
2 years 2 mons 3 days 04:05:06 (1 row)单词太复杂？记不住？
test=# select interval '1 y 2 mon 2d 12:09:12'; interval -------------------------------
1 year 2 mons 2 days 12:09:12 (1 row) test=# select interval '1 y 2 mon 2d 12h 09m 12s'; interval -------------------------------
1 year 2 mons 2 days 12:09:12 (1 row)
几个特殊日期和时间
以下是一些时间运算的示例：
test=# select timestamp(1) without time zone ‘2016-07-08 12:00:00.234’;
timestamp
———————–
2016-07-08 12:00:00.2
(1 row)
test=# select time(1) without time zone ‘2016-07-08 12:00:00.234’;
time
————
12:00:00.2
(1 row)
test=# select date'2016-07-08' - 7; ?column? ------------
2016-07-01 (1 row) test=# select date'2016-07-08' + 7; ?column? ------------
2016-07-15 (1 row) test=# test=# select date'2016-07-08' + interval'1 day 2h'; ?column? ---------------------
2016-07-09 02:00:00 (1 row) test=# select date'2016-07-08' + time'22:00'; ?column? ---------------------
2016-07-08 22:00:00 (1 row) test=# select interval'1day' + interval'1h'; ?column? ----------------
1 day 01:00:00 (1 row) test=# select timestamp'2016-07-08 22:00:00' + interval'2hour'; ?column? ---------------------
2016-07-09 00:00:00 (1 row) test=# select timestamp'2016-07-08 22:00:00' - date'2016-07-08'; ?column? ----------
22:00:00 (1 row) test=# select 10*interval'1h'; ?column? ----------
10:00:00 (1 row)
与格林威治时间相互转换
test=# select timestamp without time zone 'epoch'; timestamp --------------------- 1970-01-01 00:00:00 (1 row) test=# select timestamp without time zone 'epoch' + 3600*interval '1 sec'; ?column? --------------------- 1970-01-01 01:00:00 (1 row)
时间函数：
| 函数 | 返回类型 | 描述 | 示例 | 结果 |
| age(timestamp, timestamp) | interval | 计算两个时间戳的时间间隔 | select age(timestamp ‘2001-04-10’, timestamp ‘1957-06-13’); | 43 years 9 mons 27 days |
| age(timestamp) | interval | 计算current_date与入参时间戳的时间间隔 | select age(timestamp ‘2016-07-07 12:00:00’); | 12:00:00 |
| clock_timestamp() | timestamp with time zone | 当前时间戳（语句执行时变化） | select clock_timestamp(); | 2016-07-08 15:14:04.197732-07 |
| current_date | date | 当前日期 | select current_date; | 2016-07-08 |
| current_time | time with time zone | 当前时间 | select current_time; | 15:15:56.394651-07 |
| current_timestamp | timestamp with time zone | 当前时间戳 | select current_timestamp; | 2016-07-08 15:16:50.485864-07 |
| date_part(text, timestamp) | double precision | 获取时间戳中的某个子域，其中text可以为year,month,day,hour,minute,second等 | select date_part(‘year’,timestamp’2016-07-08 12:05:06′), date_part(‘month’,timestamp’2016-07-08 12:05:06′), date_part(‘day’,timestamp’2016-07-08 12:05:06′), date_part(‘minute’,timestamp’2016-07-08 12:05:06′), date_part(‘second’,timestamp’2016-07-08 12:05:06′); | 2016 | 7 | 8 | 12 | 5 | 6 |
| date_part(text, interval) | double precision | 功能同上，只是第二个入参为时间间隔 | select date_part(‘hour’,interval’1 day 13:00:12′); | 13 |
| date_trunc(text, timestamp) | timestamp | 将时间戳截断成指定的精度， 指定精度后面的子域用0补充 | select date_trunc(‘hour’, timestamp’2016-07-08 22:30:33′); | 2016-07-08 22:00:00 |
| date_trunc(text, interval) | interval | 功能同上，只是第二个入参为时间间隔 | select date_trunc(‘hour’,interval’1 year 2 mon 3 day 22:30:33′); | 1 year 2 mons 3 days 22:00:00 |
extract(field from timestamp) | double precision | 功能同date_part(text, timestamp) | select extract(hour from timestamp’2016-07-08 22:30:29′); | 22 |
extract(field from interval) | double precision | 功能同date_part(text, interval) | select extract(hour from interval’1 day 13:00:12′); | 13 |
| isfinite(date) | boolean | 测试是否为有穷日期 | select isfinite(date’2016-07-08′),isfinite(date’infinity’); | t,f |
| isfinite(timestamp) | boolean | 测试是否为有穷时间戳 | select isfinite(timestamp’2016-07-08′); | t |
| isfinite(interval) | boolean | 测试是否为有穷时间间隔 | select isfinite(interval’1day 23:02:12′); | t |
| justify_days(interval) | interval | 按照每月30天调整时间间隔 | select justify_days(interval’1year 45days 23:00:00′); | 1 year 1 mon 15 days 23:00:00 |
| justify_hours(interval) | interval | 按照每天24小时调整时间间隔 | select justify_hours(interval’1year 45days 343hour’); | 1 year 59 days 07:00:00 |
| justify_interval(interval) | interval | 同时使用justify_days(interval)和justify_hours(interval) | select justify_interval(interval’1year 45days 343hour’); | 1 year 1 mon 29 days 07:00:00 |
| localtime | time | 当日时间 | select localtime; | 15:45:18.892224 |
| localtimestamp | timestamp | 当日日期和时间 | select localtimestamp; | 2016-07-08 15:46:55.181583 |
| make_date(year int, month int, day int) | date | 创建一个日期 | select make_date(2016,7,8); | 2016-07-08 |
make_interval( years int DEFAULT 0, months int DEFAULT 0, weeks int DEFAULT 0, days int DEFAULT 0, hours int DEFAULT 0, mins int DEFAULT 0, secs double precision DEFAULT 0.0) | interval | 创建一个时间间隔 | select make_interval(1,hours=>3); | 1 year 03:00:00 |
make_time( hour int, min int, sec double precision) | time | 创建一个时间 | select make_time(9,21,23); | 09:21:23 |
make_timestamp( year int, month int, day int, hour int, min int, sec double precision) | timestamp | 创建一个时间戳 | select make_timestamp(2016,7,8,22,55,23.5); | 2016-07-08 22:55:23.5 |
make_timestamptz(year int, month int, day int, hour int, min int, sec double precision, [ timezone text ]) | timestamp with time zone | 创建一个带有时区的时间戳 | select make_timestamptz(2016,7,8,22,55,23.5); | 2016-07-08 22:55:23.5-07 |
| now() | timestamp with time zone | 当前日期和时间 | select now(); | 2016-07-08 15:55:30.873537-07 |
| statement_timestamp() | timestamp with time zone | 同now() | select statement_timestamp(); | 2016-07-08 15:56:07.259956-07 |
| timeofday() | text | 当前日期和时间，包含周几， 功能与clock_timestamp()类似 | select timeofday(); | Fri Jul 08 15:57:51.277239 2016 PDT |
| transaction_timestamp() | timestamp with time zone | 事务开始时的时间戳 | select transaction_timestamp(); | 2016-07-08 16:01:25.007153-07 |
| to_timestamp(double precision) | timestamp with time zone | Convert Unix epoch (seconds since 1970-01-01 00:00:00+00) to timestamp | select to_timestamp(1284352323); | 2010-09-12 21:32:03-07 |
| pg_sleep(seconds double precision); | 当前会话休眠seconds秒 | select pg_sleep(5); | ||
| pg_sleep_for(interval) | 当前会话休眠多长时间的间隔 | select pg_sleep_for(‘5 seconds’); | ||
| pg_sleep_until(timestamp with time zone) | 当前会话休眠至什么时间点 | select pg_sleep_until(‘2016-07-08 23:59:59’); |
