1:取得当前日期是本月的第几周SQL> select to_char(sysdate,'YYYYMMDD W HH24:MI:SS') from dual; TO_CHAR(SYSDATE,'YY-------------------20030327 4 18:16:09SQL> select to_char(sysdate,'W') from dual;T-42:取得当前日期是一个星期中的第几天,注意星期日是第一天SQL> select sysdate,to_char(sysdate,'D') from dual;SYSDATE T--------- -27-MAR-03 5类似:select to_char(sysdate,'yyyy') from dual; --年select to_char(sysdate,'Q' from dual; --季select to_char(sysdate,'mm') from dual; --月select to_char(sysdate,'dd') from dual; --日ddd 年中的第几天WW 年中的第几个星期W 该月中第几个星期D 周中的星期几hh 小时(12)hh24 小时(24)Mi 分ss 秒3:取当前日期是星期几中文显示:SQL> select to_char(sysdate,'day') from dual;TO_CHAR(SYSDATE,'DAY')----------------------星期四4:如果一个表在一个date类型的字段上面建立了索引，如何使用alter session set NLS_DATE_FORMAT='YYYY-MM-DD HH24:MI:SS'5: 得到当前的日期select sysdate from dual;6: 得到当天凌晨0点0分0秒的日期select trunc(sysdate) from dual;-- 得到这天的最后一秒select trunc(sysdate) + 0.99999 from dual;-- 得到小时的具体数值select trunc(sysdate) + 1/24 from dual;select trunc(sysdate) + 7/24 from dual;7.得到明天凌晨0点0分0秒的日期select trunc(sysdate+1) from dual;select trunc(sysdate)+1 from dual;8: 本月一日的日期select trunc(sysdate,'mm') from dual;9:得到下月一日的日期select trunc(add_months(sysdate,1),'mm') from dual;10:返回当前月的最后一天?select last_day(sysdate) from dual;select last_day(trunc(sysdate)) from dual;select trunc(last_day(sysdate)) from dual;select trunc(add_months(sysdate,1),'mm') - 1 from dual;11: 得到一年的每一天select trunc(sysdate,'yyyy')+ rn -1 date0from(select rownum rn from all_objectswhere rownum<366);12:今天是今年的第N天SELECT TO_CHAR(SYSDATE,'DDD') FROM DUAL;13:如何在给现有的日期加上2年select add_months(sysdate,24) from dual;14:判断某一日子所在年分是否为润年select decode(to_char(last_day(trunc(sysdate,'y')+31),'dd'),'29','闰年','平年') from dual;15:判断两年后是否为润年select decode(to_char(last_day(trunc(add_months(sysdate,24),'y')+31),'dd'),'29','闰年','平年') from dual;16:得到日期的季度select ceil(to_number(to_char(sysdate,'mm'))/3) from dual;select to_char(sysdate, 'Q') from dual;TO_DATE格式(以时间:2007-11-02 13:45:25为例)Year:yy two digits 两位年显示值:07yyy three digits 三位年显示值:007yyyy four digits 四位年显示值:2007Month:mm number 两位月显示值:11mon abbreviated 字符集表示显示值:11月,若是英文版,显示novmonth spelled out 字符集表示显示值:11月,若是英文版,显示novemberDay:dd number 当月第几天显示值:02ddd number 当年第几天显示值:02dy abbreviated 当周第几天简写显示值:星期五,若是英文版,显示friday spelled out 当周第几天全写显示值:星期五,若是英文版,显示fridayddspth spelled out, ordinal twelfthHour:hh two digits 12小时进制显示值:01hh24 two digits 24小时进制显示值:13Minute:mi two digits 60进制显示值:45Second:ss two digits 60进制显示值:25其它Q digit 季度显示值:4WW digit 当年第几周显示值:44W digit 当月第几周显示值:124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-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select to_date('2004-05-07 13:23:44','yyyy-mm-dd hh24:mi:ss') from dual//2.select to_char( to_date(222,'J'),'Jsp') from dual显示Two Hundred Twenty-Two3.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 table1UNIONselect 1, TO_DATE(null) from dual;注意要用TO_DATE(null)6.月份差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 = Americanalter 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_parametersselect * from V$NLS_PARAMETERS8.select count(*)from ( select rownum-1 rnumfrom all_objectswhere 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select months_between(to_date('01-31-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;1select months_between(to_date('02-01-1999','MM-DD-YYYY'),to_date('12-31-1998','MM-DD-YYYY')) "MONTHS" FROM DUAL;1.0322580645161310. Next_day的用法Next_day(date, day)Monday-Sunday, for format code DAYMon-Sun, for format code DY1-7, for format code D11select 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 isbeginreturn 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 offerSQL> select sysdate ,to_char(sysdate,'hh') from dual;SYSDATE TO_CHAR(SYSDATE,'HH')-------------------- ---------------------2003-10-13 19:35:21 07SQL> select sysdate ,to_char(sysdate,'hh24') from dual;SYSDATE TO_CHAR(SYSDATE,'HH24')-------------------- -----------------------2003-10-13 19:35:21 1913.年月日的处理select older_date,newer_date,years,months,abs(trunc(newer_date-add_months( older_date,years*12+months ))) daysfrom ( selecttrunc(months_between( newer_date, older_date )/12) YEARS,mod(trunc(months_between( newer_date, older_date )),12 ) MONTHS,newer_date,older_datefrom (select hiredate older_date, add_months(hiredate,rownum)+rownum newer_datefrom 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 dual16.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 0099rrrr 99 1999yyyy 01 0001rrrr 01 200118.不同时区的处理select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,sysdatefrom 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 dual2002-11-1 9:55:00 35786SSSSS表示5位秒数20.一年的第几天select TO_CHAR(SYSDATE,'DDD'),sysdate from dual310 2002-11-6 10:03:5121.计算小时,分,秒,毫秒selectDays,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)) mSecondsfrom(selecttrunc(sysdate) Days,sysdate - trunc(sysdate) Afrom dual)select * from tabnameorder 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。
