一、Date/Time Types
参考文档：https://www.postgresql.org/docs/9.2/static/datatype-datetime.html
| Types | 别名 |
|---|---|
| timestamp [ (p) ] [ without time zone ] | |
| timestamp [ (p) ] with time zone | timestamptz |
| date | |
| time [ (p) ] [ without time zone ] | |
| time [ (p) ] with time zone | |
| interval [ fields ] [ (p) ] |
注：sequelize 里常用的 DATE 类型指的是 postgres 的
timestamptz类型
二、Date/Time Input / Output
前提：postgres 的时区设置成了 PRC（中国）。
1、普通值
例：2018-08-16 20:12:16+08
//存
INSERT INTO "public"."MemberOrderLasts"("id","mobile","last_time")
VALUES
(1,'13600000000','2018-08-16 20:12:16+08');
//从库取
select "last_time" from "MemberOrderLasts" where id = '1'
//2018-08-16 20:12:16.920642+08
//直接取
select timestamp '1999-01-08 04:05:06.789+08'
//1999-01-08 04:05:06.789
select date '1999-01-08 04:05:06.789+08'
//1999-01-08
select time '1999-01-08 04:05:06.789+08'
//04:05:06.789注：即使输入带时区的时间戳，postgres 底层存的也是转换后的 UTC 时间。通过 set timezone 可以改变了数据库展示时间的方式（带时区）
2、特殊值
当在 SQL 命令中用作常量时，所有这些值都需要用单引号括起来。
| Input String | Valid Types | Description |
|---|---|---|
| epoch | date, timestamp | 1970-01-01 00:00:00+00 (Unix system time zero) |
| infinity | date, timestamp | later than all other time stamps |
| -infinity | date, timestamp | earlier than all other time stamps |
| now | date, time, timestamp | current transaction's start time |
| today | date, timestamp | midnight today |
| tomorrow | date, timestamp | midnight tomorrow |
| yesterday | date, timestamp | midnight yesterday |
| allballs | time | 00:00:00.00 UTC |
//存
INSERT INTO "public"."MemberOrderLasts"("id","mobile","last_time")
VALUES
(2,'13600000000','now');
//从库取
select "last_time" from "MemberOrderLasts" where id = '2'
//2018-09-13 14:15:12.920642+08
//直接取
select timestamp 'now'
//2018-09-13 14:29:42.27933 三、Date/Time TimeZone
1、配置文件
postgresql.conf
timezone = 'PRC'
2、postgres CLI
set timezone = 'xxx'
注意：推荐时区用 PRC、Asia/Shanghai 而不是 +08:00
因为时区和时区惯例受政治决策的影响，而不仅仅是地球几何。世界各地的时区在 20 世纪初变得有些标准化，但仍然容易发生任意变化。
四、Date/Time Functions and Operators
参考文档：https://www.postgresql.org/docs/9.2/static/functions-datetime.html
1、运算符
+ / -（* / / 不赘述，具体看文档）
select date '2018-01-12' + interval '7'
-- 2018-01-12 00:00:07
select "activatedAt" - "createdAt" AS "diff" from "Members" where id = '373'
-- 19 days 09:07:11.1552、函数
| Function | Return Type | Description | Example | Result |
|---|---|---|---|---|
age( timestamp , timestamp ) |
interval | Subtract arguments, producing a "symbolic" result that uses years and months | age(timestamp '2001-04-10', timestamp '1957-06-13') | 43 years 9 mons 27 days |
age( timestamp ) |
interval | Subtract from current_date (at midnight) |
age(timestamp '1957-06-13') | 43 years 8 mons 3 days |
date_part( text , timestamp ) |
double precision | Get subfield (equivalent to extract); see Section 9.9.1 |
date_part('hour', timestamp '2001-02-16 20:38:40') | 20 |
date_part( text , interval ) |
double precision | Get subfield (equivalent to extract); see Section 9.9.1 |
date_part('month', interval '2 years 3 months') | 3 |
date_trunc( text , timestamp ) |
timestamp | Truncate to specified precision; see also Section 9.9.2 | date_trunc('hour', timestamp '2001-02-16 20:38:40') | 2001-02-16 20:00:00 |
extract(field from timestamp ) |
double precision | Get subfield; see Section 9.9.1 | extract(hour from timestamp '2001-02-16 20:38:40') | 20 |
extract(field from interval ) |
double precision | Get subfield; see Section 9.9.1 | extract(month from interval '2 years 3 months') | 3 |
isfinite( date ) |
boolean | Test for finite date (not +/-infinity) | isfinite(date '2001-02-16') | true |
isfinite( timestamp ) |
boolean | Test for finite time stamp (not +/-infinity) | isfinite(timestamp '2001-02-16 21:28:30') | true |
isfinite( interval ) |
boolean | Test for finite interval | isfinite(interval '4 hours') | true |
justify_days( interval ) |
interval | Adjust interval so 30-day time periods are represented as months | justify_days(interval '35 days') | 1 mon 5 days |
justify_hours( interval ) |
interval | Adjust interval so 24-hour time periods are represented as days | justify_hours(interval '27 hours') | 1 day 03:00:00 |
justify_interval( interval ) |
interval | Adjust interval using justify_days and justify_hours, with additional sign adjustments |
justify_interval(interval '1 mon -1 hour') | 29 days 23:00:00 |
3、查询时间是否重叠
(start1, end1) OVERLAPS (start2, end2)
(start1, length1) OVERLAPS (start2, length2)
// `(start1, end1) OVERLAPS (start2, end2)`
SELECT (DATE '2001-02-16', DATE '2001-12-21') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
Result: true
// `(start1, length1) OVERLAPS (start2, length2)`
SELECT (DATE '2001-02-16', INTERVAL '100 days') OVERLAPS
(DATE '2001-10-30', DATE '2002-10-30');
Result: false
// 遵循左开右闭的原则
SELECT (DATE '2001-10-29', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
Result: false
SELECT (DATE '2001-10-30', DATE '2001-10-30') OVERLAPS
(DATE '2001-10-30', DATE '2001-10-31');
Result: true五、Current Date/Time
1、普通专用
（1）带时区信息
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TIME(precision)
CURRENT_TIMESTAMP(precision)
（2）不带时区信息
LOCALTIME
LOCALTIMESTAMP
LOCALTIME(precision)
LOCALTIMESTAMP(precision)
select CURRENT_TIMESTAMP
// 2018-09-13 15:10:05.639902+08
select LOCALTIMESTAMP
// 2018-09-13 15:10:05.639902还记得上面说的特殊值 now 吗，实际上跟 CURRENT_TIMESTAMP 一样：
//下面三个完全相等
SELECT CURRENT_TIMESTAMP;
SELECT TIMESTAMP 'now';
SELECT now();2、事务专用
为了保障同一事务中的多个修改具有相同的时间戳，所以 postgre 提供了针对性的时间函数：
（1） transaction_timestamp() 返回事务开始的时间
（2） statement_timestamp() 返回当前语句的开始时间
statement_timestamp() 和 transaction_timestamp() 只在一个事务的第一条命令里返回值相同
（3） clock_timestamp() 返回实际的当前时间，因此即使在单个 SQL 命令中它的值也会更改
六、Delaying Execution
pg_sleep()让当前的会话进程休眠 seconds 秒以后再执行。
SELECT pg_sleep(1.5);