20170908 oracle date to_date to_char

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select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss‘) as nowTime from dual;   //日期转化为字符串 

select to_char(sysdate,‘yyyy‘)  as nowYear   from dual;   //获取时间的年 

select to_char(sysdate,‘mm‘)    as nowMonth  from dual;   //获取时间的月 

select to_char(sysdate,‘dd‘)    as nowDay    from dual;   //获取时间的日 

select to_char(sysdate,‘hh24‘)  as nowHour   from dual;   //获取时间的时 

select to_char(sysdate,‘mi‘)    as nowMinute from dual;   //获取时间的分 

select to_char(sysdate,‘ss‘)    as nowSecond from dual;   //获取时间的秒

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select to_date(‘2004-05-07 13:23:44‘,‘yyyy-mm-dd hh24:mi:ss‘) from dual

select to_char( to_date(222,‘J‘),‘Jsp‘) from dual //显示Two Hundred Twenty-Two   

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select to_char(to_date(‘2002-08-26‘,‘yyyy-mm-dd‘),‘day‘) from dual;     //星期一    

select to_char(to_date(‘2002-08-26‘,‘yyyy-mm-dd‘),‘day‘,

‘NLS_DATE_LANGUAGE = American‘) from dual;   // monday  

//设置日期语言    

ALTER SESSION SET NLS_DATE_LANGUAGE=‘AMERICAN‘;    

//也可以这样    

TO_DATE (‘2002-08-26‘, ‘YYYY-mm-dd‘, ‘NLS_DATE_LANGUAGE = American‘)   

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select floor(sysdate - to_date(‘20020405‘,‘yyyymmdd‘)) from dual;

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select id, active_date from table1    

UNION    

select 1, TO_DATE(null) from dual;  //注意要用TO_DATE(null)   

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a_date between to_date(‘20011201‘,‘yyyymmdd‘) and to_date(‘20011231‘,‘yyyymmdd‘)    

//那么12月31号中午12点之后和12月1号的12点之前是不包含在这个范围之内的。    

//所以，当时间需要精确的时候，觉得to_char还是必要的

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alter system set NLS_DATE_LANGUAGE = American    

alter session set NLS_DATE_LANGUAGE = American    

//或者在to_date中写    

select to_char(to_date(‘2002-08-26‘,‘yyyy-mm-dd‘),

   ‘day‘,‘NLS_DATE_LANGUAGE = American‘) from dual;    

//注意我这只是举了NLS_DATE_LANGUAGE，当然还有很多，可查看    

select * from nls_session_parameters    

select * from V$NLS_PARAMETERS   

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select count(*)    

from ( select rownum-1 rnum    

   from all_objects    

   where rownum <= to_date(‘2002-02-28‘,‘yyyy-mm-dd‘) - to_date(‘2002-    

   02-01‘,‘yyyy-mm-dd‘)+1    

  )    

where to_char( to_date(‘2002-02-01‘,‘yyyy-mm-dd‘)+rnum-1, ‘D‘ )    

    not in ( ‘1‘, ‘7‘ )    

//查找2002-02-28至2002-02-01间除星期一和七的天数    

//在前后分别调用DBMS_UTILITY.GET_TIME, 让后将结果相减(得到的是1/100秒, 而不是毫秒).   

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select months_between(to_date(‘01-31-1999‘,‘MM-DD-YYYY‘),

to_date(‘12-31-1998‘,‘MM-DD-YYYY‘)) "MONTHS" FROM DUAL;    

//结果为：1    

select months_between(to_date(‘02-01-1999‘,‘MM-DD-YYYY‘),

to_date(‘12-31-1998‘,‘MM-DD-YYYY‘)) "MONTHS" FROM DUAL;    

//结果为：1.03225806451613

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Next_day(date, day)    

Monday-Sunday, for format code DAY    

Mon-Sun, for format code DY    

1-7, for format code D   

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//extract()找出日期或间隔值的字段值

SELECT EXTRACT(HOUR FROM TIMESTAMP ‘2001-02-16 2:38:40‘) from offer    

select sysdate ,to_char(sysdate,‘hh‘) from dual;    

SYSDATE               TO_CHAR(SYSDATE,‘HH‘)    

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

2003-10-13 19:35:21   07    

select sysdate ,to_char(sysdate,‘hh24‘) from dual;    

SYSDATE               TO_CHAR(SYSDATE,‘HH24‘)    

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

2003-10-13 19:35:21   19   

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SELECT

  older_date,

  newer_date,

  years,

  months,

  ABS (

    TRUNC (

      newer_date - ADD_MONTHS (older_date, years * 12 + months)

    )

  ) days

FROM

  (

    SELECT

      TRUNC (

        MONTHS_BETWEEN (newer_date, older_date) / 12

      ) YEARS,

      MOD (

        TRUNC (

          MONTHS_BETWEEN (newer_date, older_date)

        ),

        12

      ) MONTHS,

      newer_date,

      older_date

    FROM

      (

        SELECT

          hiredate older_date,

          ADD_MONTHS (hiredate, ROWNUM) + ROWNUM newer_date

        FROM

          emp

      )

  )  

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select to_char(add_months(last_day(sysdate) +1, -2), ‘yyyymmdd‘),last_day(sysdate) from dual   

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select add_months(trunc(sysdate,‘year‘), 12) - trunc(sysdate,‘year‘) from dual   

 //闰年的处理方法    

to_char( last_day( to_date(‘02‘    | | :year,‘mmyyyy‘) ), ‘dd‘ )    

 //如果是28就不是闰年

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YYYY99  TO_C    

------- ----    

yyyy 99 0099    

rrrr 99 1999    

yyyy 01 0001    

rrrr 01 2001  

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select to_char( NEW_TIME( sysdate, ‘GMT‘,‘EST‘), ‘dd/mm/yyyy hh:mi:ss‘) ,

sysdate   from dual;   

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Select TO_DATE(FLOOR(TO_CHAR(sysdate,‘SSSSS‘)/300) * 300,‘SSSSS‘) ,

TO_CHAR(sysdate,‘SSSSS‘)   from dual   

//2002-11-1 9:55:00 35786    

//SSSSS表示5位秒数   

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select TO_CHAR(SYSDATE,‘DDD‘),sysdate from dual  

//310  2002-11-6 10:03:51   

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SELECT

   Days,

   A,

   TRUNC (A * 24) Hours,

   TRUNC (A * 24 * 60 - 60 * TRUNC(A * 24)) Minutes,

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