PostgreSQL的时间/日期函数使用

PostgreSQL的常用时间函数使用整理如下：

一、获取系统时间函数

1.1 获取当前完整时间

select now();

david=# select now();
              now              
-------------------------------
 2013-04-12 15:39:40.399711+08
(1 row)

david=# 

current_timestamp 同 now() 函数等效。

david=# select current_timestamp;
              now              
-------------------------------
 2013-04-12 15:40:22.398709+08
(1 row)

david=# 

1.2 获取当前日期

select current_date;

david=# select current_date;
    date    
------------
 2013-04-12
(1 row)

david=# 

1.3 获取当前时间

select current_time;

david=# select current_time;
       timetz       
--------------------
 15:43:31.101726+08
(1 row)

david=#

二、时间的计算

david=# select now();
              now              
-------------------------------
 2013-04-12 15:47:13.244721+08
(1 row)

david=#

2.1 两年后

david=# select now() + interval ‘2 years‘;
           ?column?            
-------------------------------
 2015-04-12 15:49:03.168851+08
(1 row)

david=# select now() + interval ‘2 year‘; 
           ?column?            
-------------------------------
 2015-04-12 15:49:12.378727+08
(1 row)

david=# select now() + interval ‘2 y‘;   
           ?column?           
------------------------------
 2015-04-12 15:49:25.46986+08
(1 row)

david=# select now() + interval ‘2 Y‘;
           ?column?            
-------------------------------
 2015-04-12 15:49:28.410853+08
(1 row)

david=# select now() + interval ‘2Y‘; 
           ?column?            
-------------------------------
 2015-04-12 15:49:31.122831+08
(1 row)

david=# 

2.2 一个月后

david=# select now() + interval ‘1 month‘;  
           ?column?           
------------------------------
 2013-05-12 15:51:22.24373+08
(1 row)

david=# select now() + interval ‘one month‘;
ERROR:  invalid input syntax for type interval: "one month"
LINE 1: select now() + interval ‘one month‘;
                                ^
david=# 

2.3 三周前

david=# select now() - interval ‘3 week‘;
           ?column?            
-------------------------------
 2013-03-22 16:00:04.203735+08
(1 row)

david=# 

2.4 十分钟后

david=# select now() + ‘10 min‘;                 
           ?column?            
-------------------------------
 2013-04-12 16:12:47.445744+08
(1 row)

david=# 

说明：

interval 可以不写，其值可以是：

Abbreviation	Meaning
Y	Years
M	Months (in the date part)
W	Weeks
D	Days
H	Hours
M	Minutes (in the time part)
S	Seconds

 

 

 

 

 

2.5 计算两个时间差

使用 age(timestamp, timestamp)

david=# select age(now(), timestamp ‘1989-02-05‘);
                  age                   
----------------------------------------
 24 years 2 mons 7 days 17:05:49.119848
(1 row)

david=# 

david=# select age(timestamp ‘2007-09-15‘);       
          age           
------------------------
 5 years 6 mons 27 days
(1 row)

david=#

三、时间字段的截取

在开发过程中，经常要取日期的年，月，日，小时等值，PostgreSQL 提供一个非常便利的EXTRACT函数。

EXTRACT(field FROM source)

field 表示取的时间对象，source 表示取的日期来源，类型为 timestamp、time 或 interval。

3.1 取年份

david=# select extract(year from now());
 date_part 
-----------
      2013
(1 row)

david=# 

3.2 取月份

david=# select extract(month from now());    
 date_part 
-----------
         4
(1 row)

david=# 

david=# select extract(day from timestamp ‘2013-04-13‘);
 date_part 
-----------
        13
(1 row)

david=# 

david=# SELECT EXTRACT(DAY FROM INTERVAL ‘40 days 1 minute‘);
 date_part 
-----------
        40
(1 row)

david=# 

3.3 查看今天是一年中的第几天

david=# select extract(doy from now());
 date_part 
-----------
       102
(1 row)

david=# 

3.4 查看现在距1970-01-01 00:00:00 UTC 的秒数

david=# select extract(epoch from now());
    date_part     
------------------
 1365755907.94474
(1 row)

david=# 

3.5 把epoch 值转换回时间戳

david=# SELECT TIMESTAMP WITH TIME ZONE ‘epoch‘ + 1369755555 * INTERVAL ‘1 second‘; 
        ?column?        
------------------------
 2013-05-28 23:39:15+08
(1 row)

david=# 

以上是基本的PG时间/日期函数使用，可满足一般的开发运维应用。

 

3.6 求取两个timestamp之间的月份差

 

select 
EXTRACT(YEAR from age(‘2016-09-19 00:00:00.000000‘,  ‘2012-12-31 00:00:00.000000‘))*12+ 
EXTRACT(MONTH from age(‘2016-09-19 00:00:00.000000‘,  ‘2012-12-31 00:00:00.000000‘))

 

 

 

 

详细用法请参考：

PostgreSQL官方说明：http://www.postgresql.org/docs/9.2/static/functions-datetime.html