oracle Extract 函数

//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  

----------  

      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  

//  

 http://www.cnblogs.com/zq281660880/archive/2012/11/09/2762179.html