PostgreSQL的时间日期函数用法介绍

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

select current_date;

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

david=# 1.3

select current_time;

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

david=#二、

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

david=#2.1

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

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

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=#

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=#

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=#

--取day
skytf=> select extract(day from now());
 date_part
-----------
         3
(1 row)

skytf=> select extract(day from timestamp '2011-06-03');
 date_part
-----------
         3
(1 row)

skytf=> select timestamp '2011-06-03';
      timestamp     
---------------------
 2011-06-03 00:00:00
(1 row)

--取小时
skytf=> select extract (hour from now());
 date_part
-----------
        14
(1 row)

--取分钟
skytf=> select extract (minute from now());
 date_part
-----------
        59
(1 row)

--取秒
skytf=> select extract (second from now());
 date_part
-----------
 46.039333
(1 row)

--取所在哪个星期
skytf=> select extract (week from now());
 date_part
-----------
        22
(1 row)