Oracle Date Function 讲解和事例

请大家记住
1 year=1*12 months
1 day=24 hours=24*(1*60mins)=24*60*(1*60 seconds)
1 week =7 days注意：黑色字体是 oracle 8i，9i都可以使用的函数，蓝色字体是 Oracle9i新增的部分。请大家在使用时，注意版本限制。add_monthscurrent_date
current_timestamp
datimezoneextract(datetime)last_day
months_betweennew_time
next_day
round
SYSDATEsystimestampTO_DATE
trunc()1： Add_Months 语法： Add_Months(d,n) 函数 — n可正可负作用： Add_Months(d,n) 返回日期 D 加上n 月的日期Example:A：下个月的今天 select add_months(sysdate,1) from dual –在月份上增加

B：上个月的今天
select add_months(sysdate,-1) from dual –在月份上减少

C: 上个月的最后一天
select last_day(add_months(sysdate,-1)) from dual2: Current_date语法：Current_date作用：CURRENT_DATE 返回当前Session 时区的当前日期。Example： A：不特别设定 oracle time_zone 是和系统Time_zone 一致。select current_date,sysdate from dual SQL> select current_date,sysdate from dual ;CURRENT_DATE SYSDATE
————— —————
20051109 160535 20051109 160534 B： ALTER SESSION SET TIME_ZONE = \’-5:0\’; SQL> select current_date,sysdate from dual;CURRENT_DATE SYSDATE
————— —————
20051109 030644 20051109 1606443: Current_timestamp语法：CURRENT_TIMESTAMP（precision)作用：current_timestamp 返回此session 所在时区的当前日期和时间。数据类型是 TIMESTAMP WITH TIME ZONE.Example:A：default timestamp SQL> select CURRENT_TIMESTAMP from dual;CURRENT_TIMESTAMP
—————————————————————————
09-NOV-05 04.27.41.416811 PM +08:00
B: use precision SQL> ALTER SESSION SET TIME_ZONE =\’-5:0\’;Session altered.SQL> SELECT SESSIONTIMEZONE, CURRENT_TIMESTAMP FROM DUAL
SESSIONTIMEZONE CURRENT_TIMESTAMP
——————– ————————————————–
-05:00 09-NOV-05 03.33.32.595277 AM -05:00
C: You can user others date funtion on current_timestampSQL> select to_char(current_timestamp,\’YYYYMMDD\’) from dual; TO_CHAR(
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200511094: Dbtimezone 作用：Exreact 提取并且返回日期时间或时间间隔表达式中特定的时间域。Example:A：SELECT EXTRACT(YEAR FROM sysdate ) FROM DUALSELECT EXTRACT(YEAR FROM to_date(\’20051110\’,\’YYYYMMDD\’)) FROM DUALEXTRACT(YEARFROMTO_DATE(\’20051110\’,\’YYYYMMDD\’))
———————————————–
2005
B：SQL> SELECT EXTRACT(month FROM to_date(\’20051110\’,\’YYYYMMDD\’)) FROM DUAL;EXTRACT(MONTHFROMTO_DATE(\’20051110\’,\’YYYYMMDD\’))
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116: Last_day 语法：last_day(date)作用：last_day 返回指定日期月的最后一天 Example：SQL> SELECT SYSDATE,LAST_DAY(SYSDATE) \”Last\”,LAST_DAY(SYSDATE) – SYSDATE \”Days Left\” FROM DUAL; SYSDATE Last Days Left
——— ——— ———-
10-NOV-05 30-NOV-05 20 7：Months_between语法：Months_between(date1,date2) —(date1-date2)作用：months_between 返回两个日期间相差多少个月(Oracle default 认为31 天/month）。Example：A： select months_between(sysdate-3,sysdate) \”相差月数\”,months_between(sysdate-3,sysdate)*31 \”相差天数\” from dual 相差月数相差天数———- ———-
-.09677419 -3 （11 月只有30 天）8: New_time语法：NEW_TIME ( date , zone1 , zone2 )作用：New_time 返回在日期和时间在时区1所对应的时区2的日期和时间。（使用此函数Oracle paremeters NLS_DATE_FORMAT 必须是24 小时制）参数：Zone1 和 Zone2 参数列表1 AST, ADT: Atlantic Standard or Daylight Time
2 BST, BDT: Bering Standard or Daylight Time
3 CST, CDT: Central Standard or Daylight Time
4 EST, EDT: Eastern Standard or Daylight Time
5 GMT: Greenwich Mean Time
6 HST, HDT: Alaska-Hawaii Standard Time or Daylight Time.
7 MST, MDT: Mountain Standard or Daylight Time
8 NST: Newfoundland Standard Time
9 PST, PDT: Pacific Standard or Daylight Time
10 YST, YDT: Yukon Standard or Daylight TimeExample：SQL> SELECT NEW_TIME(sysdate,\’AST\’,\’PST\’) \”New Date and Time\”,sysdate FROM DUAL;New Date and Time SYSDATE
——————- ——————-
2005-11-10 06:24:06 2005-11-10 10:24:069： Next_day语法:NEXT_DAY ( date , char ) –根据你的 NLS_DATE_LANGUAGE 不同而不同。作用：返回从date 开始下一个 Char所对应的星期几的日期。Example:A: 下一个星期一（从sysdate 开始的下一个星期一的日期）SELECT next_day(SYSDATE,\’星期一\’) FROM dualNEXT_DAY(SYSDATE,\’星期一\’)
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05-11-14 10:48:01 B：如果你的 NLS_DATE_LANGUAGE 是 SpanishNEXT_DAY (\’01-JAN-1997\’, \’LUNES\’) ==> 06-JAN-199710: ROUND语法：ROUND (date IN DATE [, format_mask VARCHAR2]) 作用：Round 返回date 所对应格式Format_mask的日期。如果format_mask 省略则返回最近一天的日期。10.1Round 和Trunc 函数的格式

Format MaskRounds or Truncates toCC or SSCCenturySYYY, YYYY, YEAR, SYEAR, YYY, YY, or YYear (rounds up to next year on July 1)IYYY, IYY, IY, or IStandard ISO yearQQuarter (rounds up on the sixteenth day of the second month of the quarter) MONTH, MON, MM, or RMMonth (rounds up on the sixteenth day, which is not necessarily the same as the middle of the month) WWSame day of the week as the first day of the yearIWSame day of the week as the first day of the ISO yearWSame day of the week as the first day of the monthDDD, DD, or JDayDAY, DY, or DStarting day of the weekHH, HH12, HH24HourMIMinuteExample:

Round up to the next century:
Round back to the beginning of the current century:
Round down and up to the first of the year:
Round up and down to the quarter (first date in the quarter):
Round down and up to the first of the month:
Day of first of year is Saturday:
So round to date of nearest Saturday for `01-MAR-1994\’:
First day in the month is a Friday:
So round to date of nearest Friday from April 16, 1994:

使用To_char 和Round 组合显示日期：

Round back to nearest day (time always midnight):
Round forward to the nearest day:
Round back to the nearest hour:

11 TO_DATE语法：TO_DATE ( char, fmt, ’ nlsparam ’)作用：To_date 将char,varchar2,nchar或者nvarhcar2 的数据类型的字符串转换为日期类型。Fmt 表示特定格式的日期类型。Example:SELECT TO_DATE(’January 15, 1989, 11:00 A.M.’,’Month dd, YYYY, HH:MI A.M.’,’NLS_DATE_LANGUAGE = American’)
FROM DUAL;12：Trunc语法：TRUNC ( date，fmt)作用：Trunc 函数返回以特定格式(fmt) 截去某一部分的日期。(Trunc 函数的日期显示格式同ROUND 函数请参考Chart 10.1)Example：
本月的第一天
select trunc(sysdate,\’month\’) from dual本年的第一天
select trunc(sysdate,\’year\’) from dual

本月的最后一天
select last_day(sysdate) from dual
本周的第一天
select trunc(sysdate,\’day\’) from dual –Oracle default start week is Sunday
select trunc(sysdate,\’iw\’) from dual —ISO year default start week is Monday
本周的星期一
select trunc(sysdate,\’day\’)+1 from dual –2，3，4，5，6，select trunc(sysdate,\’iw\’)+1 from dual –2，3，4，5，6，

经常会用到的一些Trunc 函数例子（默认的日期格式是DD-MON-YYYY);

Without a format mask, TRUNC sets the time to 12:00 A.M. of the same day:
Trunc to the beginning of the century in all cases:
Trunc to the first of the current year:
Trunc to the first day of the quarter:
Trunc to the first of the month:

TO_Char 函数和Trunc 函数的一些组合：

Trunc back to the beginning of the current day (time is always midnight):
Trunc to the beginning of the current hour:

语法：dbtimezone作用：dbtimezone 返回数据库时区值Example:SQL> SELECT DBTIMEZONE FROM DUAL;DBTIME
——
+00:005: Extract(datetime)语法：EXTRACT (
YEAR
MONTH
DAY[@more@]

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