oracle中TO_CHAR与TO_DATE

TO_CHAR 是把日期或数字转换为字符串
TO_DATE 是把字符串转换为数据库中得日期类型转换函数 TO_DATE格式(以时间:2016-07-25   11:45:25为例)         Year:            yy two digits 两位年                显示值:16       yyy three digits 三位年                显示值:016       yyyy four digits 四位年                显示值:2016                  Month:            mm    number     两位月              显示值:07       mon    abbreviated 字符集表示         显示值:07月,若是英文版,显示jul            month spelled out 字符集表示          显示值:07月,若是英文版,显示july                Day:            dd    number         当月第几天        显示值:25       ddd    number         当年第几天        显示值:25       dy    abbreviated 当周第几天简写   显示值:星期一,若是英文版,显示mon       day    spelled out   当周第几天全写    显示值:星期一,若是英文版,显示monday            ddspth spelled out, ordinal twelfth                          Hour:              hh    two digits 12小时进制            显示值:11              hh24 two digits 24小时进制           显示值:11                           Minute:              mi    two digits 60进制                显示值:45                           Second:              ss    two digits 60进制                显示值:25                           其它              Q     digit         季度                  显示值:4              WW    digit         当年第几周            显示值:44              W    digit          当月第几周            显示值:1                    24小时格式下时间范围为:0:00:00 - 23:59:59....            12小时格式下时间范围为:1:00:00 - 12:59:59 ....           1. 日期和字符转换函数用法(to_date,to_char)        select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss') as nowTime from dual;   //日期转化为字符串  select to_char(sysdate,'yyyy') asnowYear   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   select to_date('2004-05-0713:23:44','yyyy-mm-dd hh24:mi:ss')   from dual//2.         select to_char( to_date(222,'J'),'Jsp') from dual            显示Two Hundred Twenty-Two   3.求某天是星期几       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')   4. 两个日期间的天数         select floor(sysdate - to_date('20020405','yyyymmdd')) from dual;   5. 时间为null的用法       select id, active_date from table1       UNION       select 1, TO_DATE(null) from dual;          注意要用TO_DATE(null)   6.月份差    a_date between to_date('20011201','yyyymmdd') andto_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     7. 日期格式冲突问题         输入的格式要看你安装的Oracle字符集的类型, 比如: US7ASCII, date格式的类型就是: '01-Jan-01'         alter system set NLS_DATE_LANGUAGE =American        alter session set NLS_DATE_LANGUAGE = American         或者在to_date中写        selectto_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   8.       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).   9. 查找月份       selectmonths_between(to_date('01-31-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY'))"MONTHS" FROM DUAL;        1       select months_between(to_date('02-01-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY'))"MONTHS" FROM DUAL;        1.03225806451613      10. Next_day的用法        Next_day(date, day)           Monday-Sunday, for format code DAY        Mon-Sun, for format code DY         1-7, for format code D   11.       select to_char(sysdate,'hh:mi:ss') TIME from all_objects        注意:第一条记录的TIME 与最后一行是一样的        可以建立一个函数来处理这个问题       create or replace function sys_date return date is       begin       return sysdate;        end;         select to_char(sys_date,'hh:mi:ss') from all_objects;      12.获得小时数         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        SQL> select sysdate ,to_char(sysdate,'hh') from dual;           SYSDATE TO_CHAR(SYSDATE,'HH')        -------------------- ---------------------        2003-10-13 19:35:21 07           SQL> select sysdate ,to_char(sysdate,'hh24') from dual;           SYSDATE TO_CHAR(SYSDATE,'HH24')        -------------------- -----------------------        2003-10-13 19:35:21 19         13.年月日的处理       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            )          )   14.处理月份天数不定的办法       select to_char(add_months(last_day(sysdate) +1, -2),'yyyymmdd'),last_day(sysdate) from dual   16.找出今年的天数       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   17.yyyy与rrrr的区别       'YYYY99 TO_C       ------- ----       yyyy 99 0099       rrrr 99 1999       yyyy 01 0001       rrrr 01 2001   18.不同时区的处理       select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss'),sysdate       from dual;   19.5秒钟一个间隔       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   20.一年的第几天       select TO_CHAR(SYSDATE,'DDD'),sysdate from dual         310 2002-11-6 10:03:51   21.计算小时,分,秒,毫秒        select         Days,         A,         TRUNC(A*24) Hours,         TRUNC(A*24*60 - 60*TRUNC(A*24)) Minutes,         TRUNC(A*24*60*60 - 60*TRUNC(A*24*60)) Seconds,         TRUNC(A*24*60*60*100 - 100*TRUNC(A*24*60*60)) mSeconds        from        (         select         trunc(sysdate) Days,         sysdate - trunc(sysdate) A         from dual       )      select * from tabname       order by decode(mode,'FIFO',1,-1)*to_char(rq,'yyyymmddhh24miss');         //       floor((date2-date1) /365) 作为年       floor((date2-date1, 365) /30) 作为月       d(mod(date2-date1, 365), 30)作为日.23.next_day函数      返回下个星期的日期,day为1-7或星期日-星期六,1表示星期日  next_day(sysdate,6)是从当前开始下一个星期五。后面的数字是从星期日开始算起。        12 3 4 5 6 7        日 一 二 三 四 五 六       ---------------------------------------------------------------    select   (sysdate-to_date('2003-12-03 12:55:45','yyyy-mm-ddhh24:mi:ss'))*24*60*60 from ddual   日期 返回的是天 然后转换为ss    24,round[舍入到最接近的日期](day:舍入到最接近的星期日)  select sysdate S1,  round(sysdate) S2 ,  round(sysdate,'year') YEAR,  round(sysdate,'month') MONTH ,  round(sysdate,'day') DAY from dual25,trunc[截断到最接近的日期,单位为天] ,返回的是日期类型  select sysdate S1,                        trunc(sysdate) S2,                //返回当前日期,无时分秒    trunc(sysdate,'year') YEAR,       //返回当前年的1月1日,无时分秒    trunc(sysdate,'month') MONTH ,    //返回当前月的1日,无时分秒    trunc(sysdate,'day') DAY          //返回当前星期的星期天,无时分秒   fromdual26,返回日期列表中最晚日期  select greatest('01-1月-04','04-1月-04','10-2月-04') from dual27.计算时间差     注:oracle时间差是以天数为单位,所以换算成年月,日         select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-ddhh24:mi:ss'))/365) as spanYears from dual       //时间差-年     select ceil(moths_between(sysdate-to_date('2007-11-0215:55:03','yyyy-mm-dd hh24:mi:ss'))) as spanMonths from dual        //时间差-月     select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-ddhh24:mi:ss'))) as spanDays from dual            //时间差-天     select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-ddhh24:mi:ss'))*24) as spanHours from dual        //时间差-时     select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-ddhh24:mi:ss'))*24*60) as spanMinutes from dual   //时间差-分     select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-ddhh24:mi:ss'))*24*60*60) as spanSeconds from dual //时间差-秒28.更新时间     注:oracle时间加减是以天数为单位,设改变量为n,所以换算成年月,日    select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss'),to_char(sysdate+n*365,'yyyy-mm-dd hh24:mi:ss') as newTime fromdual        //改变时间-年    select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),add_months(sysdate,n) asnewTime from dual                                 //改变时间-月     select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss'),to_char(sysdate+n,'yyyy-mm-dd hh24:mi:ss') as newTime fromdual            //改变时间-日    select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss'),to_char(sysdate+n/24,'yyyy-mm-dd hh24:mi:ss') as newTime fromdual         //改变时间-时    select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss'),to_char(sysdate+n/24/60,'yyyy-mm-dd hh24:mi:ss') as newTime fromdual      //改变时间-分    select to_char(sysdate,'yyyy-mm-ddhh24:mi:ss'),to_char(sysdate+n/24/60/60,'yyyy-mm-dd hh24:mi:ss') as newTimefrom dual   //改变时间-秒29.查找月的第一天,最后一天    SELECT Trunc(Trunc(SYSDATE, 'MONTH') - 1, 'MONTH') First_Day_Last_Month,      Trunc(SYSDATE, 'MONTH') - 1 / 86400 Last_Day_Last_Month,      Trunc(SYSDATE, 'MONTH') First_Day_Cur_Month,      LAST_DAY(Trunc(SYSDATE, 'MONTH')) + 1 - 1 / 86400 Last_Day_Cur_Month  FROM dual;

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