Friday, October 28, 2011

ORACLE SQL TUTORIAL: DATE FUNCTIONS




Ø  Sysdate
Ø  Current_date
Ø  Current_timestamp
Ø  Systimestamp
Ø  Localtimestamp
Ø  Dbtimezone
Ø  Sessiontimezone
Ø  To_char
Ø  To_date
Ø  Add_months
Ø  Months_between
Ø  Next_day
Ø  Last_day
Ø  Extract
Ø  Greatest
Ø  Least
Ø  Round
Ø  Trunc
Ø  New_time
Ø  Coalesce

Oracle default date format is DD-MON-YY.
We can change the default format to our desired format by using the following command.

SQL> alter session set nls_date_format = ‘DD-MONTH-YYYY’;
        But this will expire once the session was closed.

a) SYSDATE

     This will give the current date and time.
      Ex:
           SQL> select sysdate from dual;

SYSDATE
-----------
24-DEC-06

b) CURRENT_DATE

     This will returns the current date in the session’s timezone.

      Ex:
           SQL> select current_date from dual;

CURRENT_DATE
------------------
     24-DEC-06

c) CURRENT_TIMESTAMP

     This will returns the current timestamp with the active time zone information.

      Ex:
           SQL> select current_timestamp from dual;

CURRENT_TIMESTAMP
---------------------------------------------------------------------------
24-DEC-06 03.42.41.383369 AM +05:30

d) SYSTIMESTAMP

     This will returns the system date, including fractional seconds and time zone of the
      database.

      Ex:
           SQL> select systimestamp from dual;
SYSTIMESTAMP
---------------------------------------------------------------------------
24-DEC-06 03.49.31.830099 AM +05:30

e) LOCALTIMESTAMP

     This will returns local timestamp in the active time zone information, with no time zone
      information shown.

      Ex:
                   SQL> select localtimestamp from dual;

LOCALTIMESTAMP
---------------------------------------------------------------------------
24-DEC-06 03.44.18.502874 AM

f) DBTIMEZONE

    This will returns the current database time zone in UTC format. (Coordinated Universal Time)

    Ex:
                   SQL> select dbtimezone from dual;

DBTIMEZONE
---------------
   -07:00 

g) SESSIONTIMEZONE

    This will returns the value of the current session’s time zone.

    Ex:
         SQL> select sessiontimezone from dual;

SESSIONTIMEZONE
---------------------------------------------------------------------------
+05:30

       
       h) TO_CHAR

    This will be used to extract various date formats.
    The available date formats as follows.

    Syntax: to_char (date, format)
   
    DATE FORMATS
    
                D                             --             No of days in week
                DD                          --             No of days in month
                DDD                       --             No of days in year
                MM                       --             No of month
                MON                     --             Three letter abbreviation of month
                MONTH               --             Fully spelled out month
                RM                         --             Roman numeral month
                DY                          --             Three letter abbreviated day
                DAY                       --             Fully spelled out day
                Y                             --             Last one digit of the year
                YY                           --             Last two digits of the year
                YYY                        --             Last three digits of the year
                YYYY                     --             Full four digit year
                SYYYY   --             Signed year
                I                               --             One digit year from ISO standard
                IY                            --             Two digit year from ISO standard
                IYY                         --             Three digit year from ISO standard
                IYYY                       --             Four digit year from ISO standard
                Y, YYY                   --             Year with comma
                YEAR                     --             Fully spelled out year
                CC                           --             Century
                Q                             --             No of quarters
                W                           --             No of weeks in month
                WW                       --             No of weeks in year
                IW                          --             No of weeks in year from ISO standard
                HH                         --             Hours
                MI                          --             Minutes
                SS                           --             Seconds
                FF                           --             Fractional seconds
                AM or PM           --             Displays AM or PM depending upon time of day
                A.M or P.M         --             Displays A.M or P.M depending upon time of day
                AD or BC              --             Displays AD or BC depending upon the date
                A.D or B.C            --             Displays AD or BC depending upon the date
                FM                         --             Prefix to month or day, suppresses padding of month or day
                TH                          --             Suffix to a number
                SP                           --             suffix to a number to be spelled out
                SPTH                     --             Suffix combination of TH and SP to be both spelled out
                THSP                     --             same as SPTH

Ex:
    SQL> select to_char(sysdate,'dd month yyyy hh:mi:ss am dy') from dual;

TO_CHAR(SYSDATE,'DD MONTH YYYYHH:MI
----------------------------------------------------
24 december  2006 02:03:23 pm sun       

    SQL> select to_char(sysdate,'dd month year') from dual;


TO_CHAR(SYSDATE,'DDMONTHYEAR')
-------------------------------------------------------
24 december  two thousand six

     SQL> select to_char(sysdate,'dd fmmonth year') from dual;

TO_CHAR(SYSDATE,'DD FMMONTH YEAR')
-------------------------------------------------------
24 december two thousand six

     SQL> select to_char(sysdate,'ddth DDTH') from dual;



TO_CHAR(S
------------
24th 24TH

     SQL> select to_char(sysdate,'ddspth DDSPTH') from dual;

TO_CHAR(SYSDATE,'DDSPTHDDSPTH
------------------------------------------
twenty-fourth TWENTY-FOURTH

     SQL> select to_char(sysdate,'ddsp Ddsp DDSP ') from dual;

TO_CHAR(SYSDATE,'DDSPDDSPDDSP')
------------------------------------------------
twenty-four Twenty-Four TWENTY-FOUR

i) TO_DATE

    This will be used to convert the string into data format.

    Syntax: to_date (date)

    Ex:
         SQL> select to_char(to_date('24/dec/2006','dd/mon/yyyy'), 'dd * month * day') from
                 dual;

TO_CHAR(TO_DATE('24/DEC/20
--------------------------
24 * december  * Sunday

-- If you are not using to_char oracle will display output in default date format.
           
j) ADD_MONTHS

    This will add the specified months to the given date.

    Syntax: add_months (date, no_of_months)

    Ex:
          SQL> select add_months(to_date('11-jan-1990','dd-mon-yyyy'), 5) from dual;

ADD_MONTHS
----------------
11-JUN-90

SQL> select add_months(to_date('11-jan-1990','dd-mon-yyyy'), -5) from dual;

ADD_MONTH
---------------
11-AUG-89          

Ø  If no_of_months is zero then it will display the same date.
Ø  If no_of_months is null then it will display nothing.

k) MONTHS_BETWEEN

    This will give difference of months between two dates.

    Syntax: months_between (date1, date2)

    Ex:
         SQL> select months_between(to_date('11-aug-1990','dd-mon-yyyy'), to_date('11-jan-
                 1990','dd-mon-yyyy')) from dual;

MONTHS_BETWEEN(TO_DATE('11-AUG-1990','DD-MON-YYYY'),TO_DATE('11-JAN-1990','DD-MON-YYYY'))
-----------------------------------------------------------------------------------------------
                                                                                        7
           SQL> select months_between(to_date('11-jan-1990','dd-mon-yyyy'), to_date('11-aug-
                 1990','dd-mon-yyyy')) from dual;

MONTHS_BETWEEN(TO_DATE('11-JAN-1990','DD-MON-YYYY'),TO_DATE('11-AUG-1990','DD-MON-YYYY'))
-------------------------------------------------------------------------------------------------
                                                                                       -7

l) NEXT_DAY

    This will produce next day of the given day from the specified date.

    Syntax: next_day (date,  day)

    Ex:
         SQL> select next_day(to_date('24-dec-2006','dd-mon-yyyy'),'sun') from dual;

NEXT_DAY(
-------------
31-DEC-06

-- If the day parameter is null then it will display nothing.

m) LAST_DAY

    This will produce last day of the given date.

    Syntax: last_day (date)

    Ex:
         SQL> select last_day(to_date('24-dec-2006','dd-mon-yyyy'),'sun') from dual;

LAST_DAY(
-------------
31-DEC-06



n) EXTRACT

    This is used to extract a portion of the date value.

    Syntax: extract ((year | month | day | hour | minute | second), date)

    Ex:
         SQL> select extract(year from sysdate) from dual;
EXTRACT(YEARFROMSYSDATE)
------------------------------------
                    2006

-- You can extract only one value at a time.

o) GREATEST

     This will give the greatest date.

     Syntax: greatest (date1, date2, date3 … daten)

     Ex:
         SQL> select greatest(to_date('11-jan-90','dd-mon-yy'),to_date('11-mar-90','dd-mon-
                 yy'),to_date('11-apr-90','dd-mon-yy')) from dual;

  GREATEST(
  -------------
   11-APR-90

p) LEAST

     This will give the least date.

     Syntax: least (date1, date2, date3 … daten)

     Ex:
         SQL> select least(to_date('11-jan-90','dd-mon-yy'),to_date('11-mar-90','dd-mon-
                 yy'),to_date('11-apr-90','dd-mon-yy')) from dual;

  LEAST(
  -------------
   11-JAN-90

q) ROUND

    Round will rounds the date to which it was equal to or greater than the given date.

    Syntax: round (date, (day | month | year))


    If the second parameter was year then round will checks the month of the given date in the
    following ranges.
               
JAN        --             JUN       
                JUL         --             DEC

    If the month falls between JAN and JUN then it returns the first day of the current year.
    If the month falls between JUL and DEC then it returns the first day of the next year.

    If the second parameter was month then round will checks the day of the given date in the
    following ranges.

                1              --             15          
                16           --             31

    If the day falls between 1 and 15 then it returns the first day of the current month.
    If the day falls between 16 and 31 then it returns the first day of the next month.

    If the second parameter was day then round will checks the week day of the given date in   
    the following ranges.

                SUN       --             WED
                THU       --             SUN
    If the week day falls between SUN and WED then it returns the previous sunday.
    If the weekday falls between THU and SUN then it returns the next sunday.

Ø  If the second parameter was null then it returns nothing.
Ø  If the you are not specifying the second parameter then round will resets the time to the
     begining of the current day in case of user specified date.
Ø  If the you are not specifying the second parameter then round will resets the time to the
     begining of the next day in case of sysdate.
  
    Ex:
         SQL> select round(to_date('24-dec-04','dd-mon-yy'),'year'), round(to_date('11-mar-
                 06','dd-mon-yy'),'year') from dual;

ROUND(TO_ ROUND(TO_
------------   ---------------
01-JAN-05   01-JAN-06
           SQL> select round(to_date('11-jan-04','dd-mon-yy'),'month'), round(to_date('18-jan-
                 04','dd-mon-yy'),'month') from dual;  

ROUND(TO_ ROUND(TO_
-------------  ---------------
01-JAN-04    01-FEB-04

           SQL> select round(to_date('26-dec-06','dd-mon-yy'),'day'), round(to_date('29-dec-
                 06','dd-mon-yy'),'day') from dual;
  
ROUND(TO_ ROUND(TO_
--------------  --------------
24-DEC-06     31-DEC-06

           SQL> select to_char(round(to_date('24-dec-06','dd-mon-yy')), 'dd mon yyyy hh:mi:ss am')
                 from dual;

TO_CHAR(ROUND(TO_DATE('
---------------------------------
24 dec 2006 12:00:00 am
r) TRUNC

    Trunc will chops off the date to which it was equal to or less than the given date.

    Syntax: trunc (date, (day | month | year))

Ø  If the second parameter was year then it always returns the first day of the current year.
Ø  If the second parameter was month then it always returns the first day of the current month.
Ø  If the second parameter was day then it always returns the previous sunday.
Ø  If the second parameter was null then it returns nothing.
Ø  If the you are not specifying the second parameter then trunk will resets the time to the
      begining of the current day.

    Ex:
         SQL> select trunc(to_date('24-dec-04','dd-mon-yy'),'year'), trunc(to_date('11-mar-
                 06','dd-mon-yy'),'year') from dual;

TRUNC(TO_ TRUNC(TO_
-------------  --------------
01-JAN-04    01-JAN-06

                     SQL> select trunc(to_date('11-jan-04','dd-mon-yy'),'month'), trunc(to_date('18-jan-
                         04','dd-mon-yy'),'month') from dual;

TRUNC(TO_ TRUNC(TO_
-------------  -------------
01-JAN-04    01-JAN-04
  
  SQL> select trunc(to_date('26-dec-06','dd-mon-yy'),'day'), trunc(to_date('29-dec-06','dd- 
         mon-yy'),'day') from dual;

TRUNC(TO_ TRUNC(TO_
-------------  --------------
24-DEC-06 24-DEC-06
         
          SQL> select to_char(trunc(to_date('24-dec-06','dd-mon-yy')), 'dd mon yyyy hh:mi:ss am')
                 from dual;

TO_CHAR(TRUNC(TO_DATE('
---------------------------------
24 dec 2006 12:00:00 am

s) NEW_TIME

     This will give the desired timezone’s date and time.

     Syntax: new_time (date, current_timezone, desired_timezone)

     Available timezones are as follows.

    TIMEZONES

                                AST/ADT              --             Atlantic standard/day light time
                                BST/BDT               --             Bering standard/day light time
                                CST/CDT               --             Central standard/day light time
                                EST/EDT               --             Eastern standard/day light time
                                GMT                      --             Greenwich mean time
                                HST/HDT             --             Alaska-Hawaii standard/day light time
                                MST/MDT           --             Mountain standard/day light time
                                NST                   --  Newfoundland standard time
                                PST/PDT               --             Pacific standard/day light time
                                YST/YDT               --             Yukon standard/day light time

    Ex:
        SQL> select to_char(new_time(sysdate,'gmt','yst'),'dd mon yyyy hh:mi:ss am') from dual;

TO_CHAR(NEW_TIME(SYSDAT
-----------------------------------
24 dec 2006 02:51:20 pm

          SQL> select to_char(new_time(sysdate,'gmt','est'),'dd mon yyyy hh:mi:ss am') from dual;
TO_CHAR(NEW_TIME(SYSDAT
-----------------------
24 dec 2006 06:51:26 pm

t) COALESCE

    This will give the first non-null date.

    Syntax: coalesce (date1, date2, date3 … daten)

    Ex:
         SQL> select coalesce('12-jan-90','13-jan-99'), coalesce(null,'12-jan-90','23-mar-98',null)
                 from dual;

COALESCE( COALESCE(
-------------  ------------
12-jan-90     12-jan-90

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