postgres Date/Time 學習筆記
阿新 • • 發佈：2018-12-09
一、Date/Time Types
| Types | 別名 |
|---|---|
| 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 裡常用的 DATE 型別指的是 postgres 的
timestamptz型別
二、Date/Time Input / Output
前提：postgres 的時區設定成了 PRC（中國）。
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'); //從庫取 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：即使輸入帶時區的時間戳，postgres 底層存的也是轉換後的 UTC 時間。通過 set timezone 可以改變了資料庫展示時間的方式（帶時區）
2、特殊值
當在 SQL 命令中用作常量時，所有這些值都需要用單引號括起來。
| 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');
//從庫取
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、配置檔案
postgresql.conf
timezone = 'PRC'
2、postgres CLI
set timezone = 'xxx'
注意：推薦時區用 PRC、Asia/Shanghai 而不是 +08:00
因為時區和時區慣例受政治決策的影響，而不僅僅是地球幾何。世界各地的時區在 20 世紀初變得有些標準化，但仍然容易發生任意變化。
四、Date/Time Functions and Operators
1、運算子
+ / -（* / / 不贅述，具體看文件）
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、函式
| 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 | extract(hour from timestamp '2001-02-16 20:38:40') | 20 | |
extract(field from interval ) |
double precision | 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、查詢時間是否重疊
(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
// 遵循左開右閉的原則
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、普通專用
（1）帶時區資訊
CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP CURRENT_TIME(precision) CURRENT_TIMESTAMP(precision)
（2）不帶時區資訊
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還記得上面說的特殊值 now 嗎，實際上跟 CURRENT_TIMESTAMP 一樣：
//下面三個完全相等
SELECT CURRENT_TIMESTAMP;
SELECT TIMESTAMP 'now';
SELECT now();2、事務專用
為了保障同一事務中的多個修改具有相同的時間戳，所以 postgre 提供了針對性的時間函式：
（1） transaction_timestamp() 返回事務開始的時間
（2） statement_timestamp() 返回當前語句的開始時間
statement_timestamp() 和 transaction_timestamp() 只在一個事務的第一條命令裡返回值相同
（3） clock_timestamp() 返回實際的當前時間，因此即使在單個 SQL 命令中它的值也會更改
六、Delaying Execution
pg_sleep()讓當前的會話程序休眠 seconds 秒以後再執行。
SELECT pg_sleep(1.5);