PostgreSQL time/date functions

function	return type	describe	example	result
age(timestamp, timestamp)	interval	"Symbolicized" result after subtracting arguments, using years and months, not just days	age(timestamp '2001-04-10', timestamp '1957-06-13')	43 years 9 mons 27 days
age(timestamp)	interval	From current_datethe result after subtracting the argument (at midnight)	age(timestamp '1957-06-13')	43 years 8 mons 3 days
clock_timestamp()	timestamp with time zone	The current timestamp of the real-time clock (changes as the statement executes)
current_date	date	the current date;
current_time	time with time zone	time of day;
current_timestamp	timestamp with time zone	Timestamp when the current transaction started;
date_part(text, timestamp)	double precision	get subdomain (equivalent to extract);	date_part('hour', timestamp '2001-02-16 20:38:40')	20
date_part(text, interval)	double precision	get subdomain (equivalent to extract);	date_part('month', interval '2 years 3 months')	3
date_trunc(text, timestamp)	timestamp	truncate to the specified precision;	date_trunc('hour', timestamp '2001-02-16 20:38:40')	2001-02-16 20:00:00
date_trunc(text, interval)	interval	intercept to the specified precision,	date_trunc('hour', interval '2 days 3 hours 40 minutes')	2 days 03:00:00
extract(field from timestamp)	double precision	get subdomain;	extract(hour from timestamp '2001-02-16 20:38:40')	20
extract(field from interval)	double precision	get subdomain;	extract(month from interval '2 years 3 months')	3
isfinite(date)	boolean	Test for finite date (not +/- infinite)	isfinite(date '2001-02-16')	true
isfinite(timestamp)	boolean	Test for finite timestamps (not +/- infinity)	isfinite(timestamp '2001-02-16 21:28:30')	true
isfinite(interval)	boolean	test whether it is a finite time interval	isfinite(interval '4 hours')	true
justify_days(interval)	interval	Adjust the time interval by 30 days per month	justify_days(interval '35 days')	1 mon 5 days
justify_hours(interval)	interval	Adjust the time interval according to 24 hours a day	justify_hours(interval '27 hours')	1 day 03:00:00
justify_interval(interval)	interval	Sign adjustments while using justify_daysand adjusting time intervalsjustify_hours	justify_interval(interval '1 mon -1 hour')	29 days 23:00:00
localtime	time	time of day;
localtimestamp	timestamp	Timestamp when the current transaction started;
make_date(year int, month int, day int)	date	Create a date for the year, month and day fields	make_date(2013, 7, 15)	2013-07-15
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	Create intervals from year, month, week, day, hour, minute and second fields	make_interval(days := 10)	10 days
make_time(hour int, min int, sec double precision)	time	Create time from hours, minutes and seconds fields	make_time(8, 15, 23.5)	08:15:23.5
make_timestamp(year int, month int, day int, hour int, min int, sec double precision)	timestamp	Create timestamps from year, month, day, hour, minute and second fields	make_timestamp(2013, 7, 15, 8, 15, 23.5)	2013-07-15 08:15:23.5
make_timestamptz(year int, month int, day int, hour int, min int, sec double precision, [ timezone text ])	timestamp with time zone	Create a timestamp with time zone from the year, month, day, hour, minute and second fields. When no timezone is specified, the current timezone is used.	make_timestamptz(2013, 7, 15, 8, 15, 23.5)	2013-07-15 08:15:23.5+01
now()	timestamp with time zone	当前事务开始时的时间戳；
statement_timestamp()	timestamp with time zone	实时时钟的当前时间戳；
timeofday()	text	与clock_timestamp相同，但结果是一个text 字符串；
transaction_timestamp()	timestamp with time zone	当前事务开始时的时间戳；