Oracle extract 函數及過濾查詢到的重複數據

select distinct fieldName from tableName　　--利用distinct來過濾

oracle Extract 函數 
//oracle中extract()函數從oracle 9i中引入,用於從一個date或者interval類型中截取到特定的部分    
//語法如下：    
EXTRACT (    
        { YEAR | MONTH | DAY | HOUR | MINUTE | SECOND }    
        | { TIMEZONE_HOUR | TIMEZONE_MINUTE }    
        | { TIMEZONE_REGION | TIMEZONE_ABBR }    
FROM { date_value | interval_value } )    
//我們只可以從一個date類型中截取 year,month,day(date日期的格式爲yyyy-mm-dd);    
//我們只可以從一個 timestamp with time zone 的數據類型中截取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    
//獲取兩個日期之間的具體時間間隔，extract函數是最好的選擇    
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    
//