Conversion of Oracle date

to_date()

to_date(" String to convert "," Converted format ") The format of the two parameters must match , Otherwise, an error will be reported .
That is, the first parameter is interpreted according to the format of the second parameter .

to_char( date ," Transformation format " ) That is, according to the given date “ Transformation format ” transformation .

Converted format ：

• Express year Of ：y The last person of the year yy At the end of the year 2 position yyy At the end of the year 3 position yyyy use 4 The number of digits represents the year
• Express month Of ：mm use 2 A digit represents the month ;mon In short form such as 11 Month or nov ;month In full name such as 11 Month or november
• Express day Of ：dd It means the day of the month ;ddd The first day of the year ;dy What day of the week Abbreviation Like Friday or fri;day What day of the week Full write
  Like Friday or friday.
• Express hour Of ：hh 2 The number of digits represents the hour 12 Base number ; hh24 2 The number of digits represents the hour 24 Hours
• Express minute Of ：mi 2 The number of digits represents minutes
• Express second Of ：ss 2 The number of digits represents seconds 60 Base number
• It's a quarter ：q One digit It means quarter （1-4）
• And then there is ww Used to indicate the week of the year w Used to indicate the week of the month .
• 24 The time range in the hour system ：00：00：00-23：59：59
• 12 The time range in the hour system ：1：00：00-12：59：59

such as ：

select to_char(sysdate,'yy-mm-dd hh24:mi:ss') from dual   // Show ：08-11-07 13:22:42

select to_date('2005-12-25,13:25:59','yyyy-mm-dd,hh24:mi:ss') from dual // Show ：2005-12-25 13:25:59

And if you write in the above form ：select to_date('2005-12-25,13:25:59','yyyy-mm-dd,hh:mi:ss') from dual, May be an error , Because hours hh yes 12 Base number ,13 For illegal input , Can't match .

Add ：

 Subtract... From the current time 7 Minutes of time  
select sysdate,sysdate - interval '7' MINUTE from dual 
 Subtract... From the current time 7 Hours of time  
select sysdate - interval '7' hour from dual 
 Subtract... From the current time 7 Time of day  
select sysdate - interval ’7’ day from dual 
 Subtract... From the current time 7 Time of the month  
select sysdate,sysdate - interval '7' month from dual 
 Subtract... From the current time 7 Years of time  
select sysdate,sysdate - interval '7' year from dual 
 Multiply the time interval by a number  
select sysdate,sysdate - 8*interval '7' hour from dual

Dual Pseudo column

Explanation of meaning ：

Dual yes Oracle An actual table in , Any user can read , It's often used when there's no target table select In the block .

such as , I want to get system time , Then use “select sysdate from dual” Then return to the current time of the system ：2008-11-07 9:32:49, Different systems may return dates in different formats .“select user from dual" Then return the currently connected user . If it is "select 1+2 from dual”, Returns the result ：3

come from :http://hi.baidu.com/xkf007/blog/item/eb21d983b92e78b30cf4d2a5.html

TO_DATE Format ( In time :2007-11-02 13:45:25 For example )

Year:
yy two digits Two years Display value :07
yyy three digits Three years Display value :007
yyyy four digits Four years Display value :2007

Month:      
mm    number      Two months                Display value :11
mon    abbreviated  The character set represents            Display value :11 month , If it's in English , Show nov     
month spelled out  The character set represents            Display value :11 month , If it's in English , Show november 
  
Day:      
dd    number          What day of the month          Display value :02
ddd    number          The first few days of that year          Display value :02
dy    abbreviated  The day of the week      Display value : Friday , If it's in English , Show fri
day    spelled out    What day of the week is it all written      Display value : Friday , If it's in English , Show friday        
ddspth spelled out, ordinal twelfth 
     
      Hour:
      hh    two digits 12 Hourly system              Display value :01
      hh24 two digits 24 Hourly system              Display value :13
      
      Minute:
      mi    two digits 60 Base number                  Display value :45
      
      Second:
      ss    two digits 60 Base number                  Display value :25
      
       Other 
      Q     digit          quarter                    Display value :4
      WW    digit          In the first few weeks of that year              Display value :44
      W    digit           What week of the month              Display value :1
      
24 The time range in the hour format is ： 0:00:00 - 23:59:59....      
12 The time range in the hour format is ： 1:00:00 - 12:59:59 .... 

1. Date and character conversion function usage （to_date,to_char）

select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') as nowTime from dual;   // The date is converted to a string  
select to_char(sysdate,'yyyy') as nowYear   from dual;   // The year to get time  
select to_char(sysdate,'mm')    as nowMonth from dual;   // Get the month of time  
select to_char(sysdate,'dd')    as nowDay    from dual;   // Get the day of time  
select to_char(sysdate,'hh24') as nowHour   from dual;   // The time to get time  
select to_char(sysdate,'mi')    as nowMinute from dual;   // Get the minutes of time  
select to_char(sysdate,'ss')    as nowSecond from dual;   // Get the seconds of time 
    
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

Show Two Hundred Twenty-Two

3. Ask what day of the week it is

 select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day') from dual;      
    Monday       
   select to_char(to_date('2002-08-26','yyyy-mm- dd'),'day','NLS_DATE_LANGUAGE = American') from dual;      
   monday      
    Set the date language       
   ALTER SESSION SET NLS_DATE_LANGUAGE='AMERICAN';      
    You can do that       
   TO_DATE ('2002-08-26', 'YYYY-mm-dd', 'NLS_DATE_LANGUAGE = American')    

4. The number of days between two dates

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

5. Time is null Usage of

select id, active_date from table1      
   UNION      
   select 1, TO_DATE(null) from dual;      
   
    Pay attention to TO_DATE(null)    

6. Month difference

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

that 12 month 31 At noon, 12 After two o'clock and 12 month 1 The no. 12 Before the point is not included in this range .
therefore , When time needs to be precise , Think to_char It's still necessary

7. Date format conflict
   The input format depends on what you install ORACLE The type of character set , such as : US7ASCII, date The type of format is : ‘01-Jan-01’

 alter system set NLS_DATE_LANGUAGE = American      
    alter session set NLS_DATE_LANGUAGE = American      
     Or in to_date Write in       
    select to_char(to_date('2002-08-26','yyyy-mm-dd'),'day','NLS_DATE_LANGUAGE = American') from dual;      
     Notice that I'm just raising NLS_DATE_LANGUAGE, Of course, there are a lot more ,      
     You can see       
    select * from nls_session_parameters      
    select * from V$NLS_PARAMETERS    

  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' )      

lookup 2002-02-28 to 2002-02-01 Days between Monday and seven
Call... Before and after DBMS_UTILITY.GET_TIME, Let's subtract the results from each other ( Get is 1/100 second , Not milliseconds ).

9. Find the month

 select months_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 Usage of

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      
    Be careful ： The first record TIME  It's the same as the last line       
    You can build a function to deal with this       
   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. Get hours

extract() Find the field value of the date or interval value
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. The date of processing

 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. The way to deal with the uncertainty of months and days

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

16. Find out the number of days this year

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

How to deal with leap years

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

If it is 28 It's not a leap year

17.yyyy And rrrr The difference between

  'YYYY99 TO_C      
   ------- ---- 
   yyyy 99 0099      
   rrrr 99 1999      
   yyyy 01 0001      
   rrrr 01 2001    

18. Processing of different time zones

  select to_char( NEW_TIME( sysdate, 'GMT','EST'), 'dd/mm/yyyy hh:mi:ss') ,sysdate      
   from dual;    

19.5 Every second

  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 Express 5 Bit seconds

20. The day of the year

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

310 2002-11-6 10:03:51

21. Calculating hours , branch , second , millisecond

    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) As a year
floor((date2-date1, 365) /30) As a month
d(mod(date2-date1, 365), 30) As a day .

23.next_day function Return to next week's date ,day by 1-7 Or Sunday - Saturday ,1 Means Sunday
next_day(sysdate,6) It's the next Friday from now on . The following figures start from Sunday .
1 2 3 4 5 6 7
Japan One Two 3、 ... and Four 5、 ... and 6、 ... and

---

select    (sysdate-to_date('2003-12-03 12:55:45','yyyy-mm-dd hh24:mi:ss'))*24*60*60 from ddual

date It's the day back then Convert to ss

24,round Round to the nearest date

select sysdate S1,
   round(sysdate) S2 ,
   round(sysdate,'year') YEAR,
   round(sysdate,'month') MONTH ,
   round(sysdate,'day') DAY from dual

25,trunc[ Truncate to the nearest date , The unit is days ] , The date type is returned

select sysdate S1,                     
     trunc(sysdate) S2,                 // Return current date , No time, no minutes, no seconds 
     trunc(sysdate,'year') YEAR,        // Return to... Of the current year 1 month 1 Japan , No time, no minutes, no seconds 
     trunc(sysdate,'month') MONTH ,     // Returns... Of the current month 1 Japan , No time, no minutes, no seconds 
     trunc(sysdate,'day') DAY           // Return to the Sunday of the current week , No time, no minutes, no seconds 
   from dual

26, Returns the latest date in the date list

select greatest('01-1 month -04','04-1 month -04','10-2 month -04') from dual

27. Calculate the time difference
notes :oracle The time difference is in days , So, in terms of months , Japan

  select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))/365) as spanYears from dual        // Time difference - year 
  select ceil(moths_between(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))) as spanMonths from dual        // Time difference - month 
  select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))) as spanDays from dual             // Time difference - God 
  select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24) as spanHours from dual         // Time difference - when 
  select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24*60) as spanMinutes from dual    // Time difference - branch 
  select floor(to_number(sysdate-to_date('2007-11-02 15:55:03','yyyy-mm-dd hh24:mi:ss'))*24*60*60) as spanSeconds from dual // Time difference - second 

28. Update time
> notes :oracle Time addition and subtraction are in days , Let the change be n, So, in terms of months , Japan

select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),to_char(sysdate+n*365,‘yyyy-mm-dd hh24:mi:ss’) as newTime from dual // Change time - year
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),add_months(sysdate,n) as newTime from dual // Change time - month
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),to_char(sysdate+n,‘yyyy-mm-dd hh24:mi:ss’) as newTime from dual // Change time - Japan
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),to_char(sysdate+n/24,‘yyyy-mm-dd hh24:mi:ss’) as newTime from dual // Change time - when
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),to_char(sysdate+n/24/60,‘yyyy-mm-dd hh24:mi:ss’) as newTime from dual // Change time - branch
select to_char(sysdate,‘yyyy-mm-dd hh24:mi:ss’),to_char(sysdate+n/24/60/60,‘yyyy-mm-dd hh24:mi:ss’) as newTime from dual // Change time - second

29. Find the first day of the month , The last day

     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;