PostgreSQL 时间/日期函数的使用组织如下

PostgreSQL 中常用的时间函数组织如下：

1。获取系统时间函数

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 与now()函数等效。

david=# select current_timestamp;
              now              
-------------------------------
 2013-04-12 15:40:298709+08
(1 row)

david=#

获取当前日期

select current_date;

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

david=#

获取当前时间

select current_time;

david=# select current_time;
       timetz       
--------------------
 15:43:301726+08
(1 row)

david=#

2.计算时间稍后一个月后

david=# select now() + interval '1 month';  
           ?column?           
------------------------------
 2013-05-12 15:51:24373+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=#

3周前 十分钟后

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

david=#

注：

间隔不需要写，取值可以是：

EXTRACT(field FROM source)

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

david=#

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=#

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

david=#

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

david=#

select 
EXTRACT(YEARfrom age('2016-09-19 00:00:',  '2012-12-31 00:00:'))*12+ 
EXTRACT(MONTHfrom age('2016-09-19 00:00:',  '2012-12-31 00:00:'))