Oracle EXTRACT()函数(转载)

oracle中extract()函数从oracle 9i中引入,用于从一个date或者interval类型中截取到特定的部分  

//语法如下：  

EXTRACT (  

        { YEAR | MONTH | DAY | HOUR | MINUTE | SECOND }  

        | { TIMEZONE_HOUR | TIMEZONE_MINUTE }  

        | { TIMEZONE_REGION | TIMEZONE_ABBR } 

FROM { date_value | interval_value } )  

//我们只可以从一个date类型中截取 year,month,day(date日期的格式为yyyy-mm-dd);  

//我们只可以从一个 timestamp with time zone 的数据类型中截取TIMEZONE_HOUR和TIMEZONE_MINUTE;  

select extract(year from date'2011-05-17') year from dual;  

      YEAR  

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----------  

      2011  

select extract(month from date'2011-05-17') month from dual;  

    MONTH  

----------  

        5  

select extract(day from date'2011-05-17') day from dual;  

      DAY  

----------  

        17  

//获取两个日期之间的具体时间间隔，extract函数是最好的选择  

select extract(day from dt2-dt1) day  

      ,extract(hour from dt2-dt1) hour  

      ,extract(minute from dt2-dt1) minute  

      ,extract(second from dt2-dt1) second  

from (  

    select to_timestamp('2011-02-04 15:07:00','yyyy-mm-dd hh24:mi:ss') dt1  

          ,to_timestamp('2011-05-17 19:08:46','yyyy-mm-dd hh24:mi:ss') dt2  

    from dual)  

/  

      DAY      HOUR    MINUTE    SECOND  

---------- ---------- ---------- ----------  

      102          4          1        46  

--  

select extract(year from systimestamp) year  

      ,extract(month from systimestamp) month  

      ,extract(day from systimestamp) day  

      ,extract(minute from systimestamp) minute  

      ,extract(second from systimestamp) second 

      ,extract(timezone_hour from systimestamp) th  

      ,extract(timezone_minute from systimestamp) tm  

      ,extract(timezone_region from systimestamp) tr  

      ,extract(timezone_abbr from systimestamp) ta  

from dual  

/  

    YEAR      MONTH        DAY    MINUTE    SECOND        TH        TM TR        TA  

---------- ---------- ---------- ---------- ---------- ---------- ---------- --------- ----------  

      2011          5        17          7    14.843          8          0 UNKNOWN  UNK