postgresql----时间类型

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
函数	interval	计算两个时间戳的时间间隔	select age(timestamp ‘2001-04-10’,	43 years 9 mons 27 days
			timestamp ‘1957-06-13’);
age(timestamp)	interval	计算current_date与入参时间戳的时间间隔	select age(timestamp	12:00:00
			‘2016-07-07 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;	2016/7/8
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’),	2016
			date_part(‘month’,timestamp’2016-07-08 12:05:06’),
			date_part(‘day’,timestamp’2016-07-08 12:05:06’),
			date_part(‘hour’,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’);
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，	select date_trunc(‘hour’,	2016/7/8 22:00
		指定精度后面的子域用0补充	timestamp’2016-07-08 22:30:33’);
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;	45:18.9
localtimestamp	timestamp	当日日期和时间	select localtimestamp;	46:55.2
make_date(year int, month int, day int)	date	创建一个日期	select make_date(2016,7,8);	2016/7/8
make_interval(	interval	创建一个时间间隔	select make_interval(1,hours=>3);	1 year 03:00:00
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)
make_time(	time	创建一个时间	select make_time(9,21,23);	9:21:23
hour int,
min int,
sec double precision)
make_timestamp(	timestamp	创建一个时间戳	select make_timestamp(2016,7,8,22,55,23.5);	55:23.5
year int, month int,
day int, hour int,
min int,
sec double precision)
make_timestamptz(year int,	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
month int,
day int, hour int,
min int, sec double precision, [ timezone text ])
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，	select timeofday();	fri jul 08 15:57:51.277239 2016 pdt
		功能与clock_timestamp()类似
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	select to_timestamp(1284352323);	2010-09-12 21:32:03-07
		(seconds since 1970-01-01
		00:00:00+00) to timestamp
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’);