PostgreSQL的时间/日期函数使用

朴灿烈づ我的快乐病毒、 2022-06-05 08:00 645阅读 0赞

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();

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

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current\_timestamp 同 now() 函数等效。

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

![复制代码][copycode.gif]

1.2 获取当前日期

select current\_date;

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

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1.3 获取当前时间

select current\_time;

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

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二、时间的计算

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

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2.1 两年后

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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=#

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2.2 一个月后

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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=#

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2.3 三周前

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

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2.4 十分钟后

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

![复制代码][copycode.gif]

说明：

interval 可以不写，其值可以是：

<table style="margin:0px; padding:0px; border:1px solid silver; border-collapse:collapse; word-break:break-word; color:rgb(51,51,51); font-family:verdana,Arial,Helvetica,sans-serif; font-size:14px; line-height:25.2px"> 
 <tbody style="margin:0px; padding:0px"> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Abbreviation</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Meaning</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Y</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Years</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> M</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Months (in the date part)</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> W</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Weeks</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> D</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Days</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> H</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Hours</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> M</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Minutes (in the time part)</td> 
 </tr> 
 <tr style="margin:0px; padding:0px"> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S</td> 
 <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Seconds</td> 
 </tr> 
 </tbody> 
</table>

2.5 计算两个时间差

使用 age(timestamp, timestamp)

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

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

![复制代码][copycode.gif]

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

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

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3.2 取月份

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

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

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

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3.3 查看今天是一年中的第几天

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

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3.4 查看现在距1970-01-01 00:00:00 UTC 的秒数

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

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3.5 把epoch 值转换回时间戳

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

![复制代码][copycode.gif]

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。

详细用法请参考：

PostgreSQL官方说明：[http://www.postgresql.org/docs/9.2/static/functions-datetime.html][http_www.postgresql.org_docs_9.2_static_functions-datetime.html]

原文网址：https://www.cnblogs.com/mchina/archive/2013/04/15/3010418.html

[copycode.gif]: /images/20220605/1c8d6e0546b14441b5549b2d27545b94.png
[http_www.postgresql.org_docs_9.2_static_functions-datetime.html]: http://www.postgresql.org/docs/9.2/static/functions-datetime.html