--把时间戳转成epoch值
postgres=# select extract(epoch from now());
date_part
------------------
1447898857.74524
(1 row)
--把epoch 值转换回时间戳
postgres=# SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 1447898857.74524 * INTERVAL '1 second';
?column?
------------------------------
2015-11-19 10:07:37.74524+08
postgres=# SELECT TIMESTAMP WITH TIME ZONE 'epoch' + 1447898857.74524 * INTERVAL '1 second';
?column?
------------------------------
2015-11-19 10:07:37.74524+08
--查看当前的时间戳
postgres=# select clock_timestamp(),current_timestamp,localtimestamp;
clock_timestamp | now | timestamp
-------------------------------+-------------------------------+----------------------------
2016-02-02 17:54:15.547194+08 | 2016-02-02 17:54:15.546956+08 | 2016-02-02 17:54:15.546956
--时间加减
postgres=# select date '2016-02-02 10:00:00'+ interval '10 minutes';
?column?
---------------------
2016-02-02 00:10:00
--直接用sql生成随机日期时间
select '2015-5-1'::date + trunc(random()*100)::integer +' 00:22:22'::time + (trunc(random()*3600*24)||' second')::interval;
--不同时区之间的转换
postgres=# select '2016-02-03 09:07:30.816885+08' at time zone 'pst';
timezone
----------------------------
2016-02-02 17:07:30.816885
(1 row)
postgres=# select '2016-02-03 09:07:30.816885+08' at time zone 'cct';
timezone
----------------------------
2016-02-03 09:07:30.816885
(1 row)
postgres=# SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'cct';
timezone
---------------------
2001-02-17 09:38:40
--查看系统支持的时区
select * from pg_timezone_names ;
--时区设置参数
timezone = 'PRC'
--修改时区的方法
1. 全局参数
postgresql.conf
timezone='UTC'
2. 数据库级配置
alter database dbname set timezone='UTC';
pipeline=# select * from pg_db_role_setting ;
setdatabase | setrole | setconfig
-------------+---------+--------------------------------------
14930 | 0 | {TimeZone=UTC}
3. 用户级配置
alter role rolname set timezone='UTC';
或者
alter role all set timezone='UTC';
pipeline=# select * from pg_db_role_setting ;
setdatabase | setrole | setconfig
-------------+---------+--------------------------------------
14930 | 0 | {TimeZone=UTC}
0 | 0 | {TimeZone=UTC}
--创建随机日期时间函数
CREATE OR REPLACE FUNCTION rand_date_time(start_date date, end_date date) RETURNS TIMESTAMP AS
$BODY$
DECLARE
interval_days integer;
random_seconds integer;
random_dates integer;
random_date date;
random_time time;
BEGIN
interval_days := end_date - start_date;
random_dates:= trunc(random()*interval_days);
random_date := start_date + random_dates;
random_seconds:= trunc(random()*3600*24);
random_time:=' 00:00:00'::time+(random_seconds || ' second')::INTERVAL;
RETURN random_date +random_time;
END;
$BODY$
LANGUAGE plpgsql;
--生成指定时间内的随机时间
SELECT rand_date_time('2000-01-01', '2013-12-31');
--休眠1.5秒后执行,单位秒
SELECT clock_timestamp(),pg_sleep(1.5),clock_timestamp();
--休眠5分钟,单位interval
SELECT clock_timestamp(),pg_sleep_for('5 minutes'),clock_timestamp();
--到指定时间执行,注意这些休眠时间不是完全精确的
SELECT clock_timestamp(),pg_sleep_until('today 10:00'),clock_timestamp();