How to handle date time in Oracle sql quries OCA, OCP track class in sri lanka colombo

EXTRACT (datetime)

Syntax

extract_datetime::=

Description of the illustration extract_datetime.gif

Purpose

EXTRACT extracts and returns the value of a specified datetime field from a datetime or interval value expression. When you extract a TIMEZONE_REGION orTIMEZONE_ABBR (abbreviation), the value returned is a string containing the appropriate time zone name or abbreviation. When you extract any of the other values, the value returned is in the Gregorian calendar. When extracting from a datetime with a time zone value, the value returned is in UTC. For a listing of time zone names and their corresponding abbreviations, query the V$TIMEZONE_NAMES dynamic performance view.

This function can be very useful for manipulating datetime field values in very large tables, as shown in the first example below.

Note:

Timezone region names are needed by the daylight savings feature. The region names are stored in two time zone files. The default time zone file is a small file containing only the most common time zones to maximize performance. If your time zone is not in the default file, then you will not have daylight savings support until you provide a path to the complete (larger) file by way of the ORA_TZFILE environment variable.

Some combinations of datetime field and datetime or interval value expression result in ambiguity. In these cases, Oracle Database returns UNKNOWN (see the examples that follow for additional information).

The field you are extracting must be a field of the datetime_value_expr or interval_value_expr. For example, you can extract only YEAR, MONTH, and DAY from a DATE value. Likewise, you can extract TIMEZONE_HOUR and TIMEZONE_MINUTE only from the TIMESTAMP WITH TIME ZONE datatype.

See Also:

• Oracle Database Administrator's Guide for more information about setting the ORA_TZFILE environment variable
• Oracle Database Globalization Support Guide. for a complete listing of the timezone region names in both files
• "Datetime/Interval Arithmetic" for a description of datetime_value_expr and interval_value_expr
• Oracle Database Reference for information on the dynamic performance views

Examples

The following example returns from the oe.orders table the number of orders placed in each month:

SELECT EXTRACT(month FROM order_date) "Month",
  COUNT(order_date) "No. of Orders"
  FROM orders
  GROUP BY EXTRACT(month FROM order_date)
  ORDER BY "No. of Orders" DESC;

     Month No. of Orders
---------- -------------
        11            15
         7            14
         6            14
         3            11
         5            10
         9             9
         2             9
         8             7
        10             6
         1             5
        12             4
         4             1
 
12 rows selected.

The following example returns the year 1998.

SELECT EXTRACT(YEAR FROM DATE '1998-03-07') FROM DUAL;

EXTRACT(YEARFROMDATE'1998-03-07')
---------------------------------
                             1998

The following example selects from the sample table hr.employees all employees who were hired after 1998:

SELECT last_name, employee_id, hire_date
   FROM employees
   WHERE EXTRACT(YEAR FROM
   TO_DATE(hire_date, 'DD-MON-RR')) > 1998
   ORDER BY hire_date;


LAST_NAME                 EMPLOYEE_ID HIRE_DATE
------------------------- ----------- ---------
Landry                            127 14-JAN-99
Lorentz                           107 07-FEB-99
Cabrio                            187 07-FEB-99
. . .

The following example results in ambiguity, so Oracle returns UNKNOWN:

SELECT EXTRACT(TIMEZONE_REGION 
      FROM TIMESTAMP '1999-01-01 10:00:00 -08:00')
   FROM DUAL;

EXTRACT(TIMEZONE_REGIONFROMTIMESTAMP'1999-01-0110:00:00-08:00')
----------------------------------------------------------------
UNKNOWN

The ambiguity arises because the time zone numerical offset is provided in the expression, and that numerical offset may map to more than one time zone region.

Reference - http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions050.htm

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Date & Time Functions
MySQL date and time functions can be used to change the value of date and time columns.

ADDDATE( ) This MySQL function can be used to add a given interval of time to a date or the value of a date column	ADDTIME( ) Similar to ADDDATE(), but specifically and supposedly for adding time to a value. However, both MySQL functions allow the addition of date and time to a value.
CONVERT_TZ( ) This MySQL function converts a date and time for given time zone to another which is specified.	CURDATE( ) This MySQL function returns the current system date in yyyy-mm-dd format.
CURRENT_DATE( ) This MySQL function is the same as CURDATE().	CURRENT_TIME( ) This MySQL function returns the current time in hh:mm:ss format. This is synonymous with CURTIME( ).
CURRENT_TIMESTAMP( ) This MySQL function returns the current date and time in yyyy-mm-dd hh:mm:ss format.	CURTIME( ) This MySQL function returns the current system time in hh:mm:ss format.
DATE( ) This MySQL function returns the date from a given string, value, or expression that is submitted in a date or datetime format.	DATEDIFF( ) This MySQL function returns the number of days of difference between the two dates given.
DATE_ADD( ) Using the date or datetime given, this MySQL function adds the number of intervals specified. It's fairly synonymous with the ADDDATE( ) function.	DATE_FORMAT( ) This MySQL function returns a date and time in a desired format, based on formatting codes listed within quotes for the second argument of the function.
DATE_SUB( ) Use this MySQL function to subtract from the results of a date or time data type column. It's fairly synonymous with the SUBDATE( ).	DAY( ) This MySQL function returns the day of the month for a given date.
DAYNAME( ) This MySQL function returns the name of the day for the date provided.	DAYOFMONTH( ) This MySQL function returns the day of the month for the date given.
DAYOFWEEK( ) This MySQL function returns the numerical day of the week for a given date.	DAYOFYEAR( ) This MySQL function returns the day of the year. January 1 would give a value of 1.
EXTRACT( ) This MySQL function extracts date or time information from a date or a datetime expression in the format type requested.	FROM_DAYS( ) This MySQL function returns the date based on the number of days given, which are from the beginning of the currently used standard calendar.
FROM_UNIXTIME( ) This MySQL function returns the date based on Unix time, which is the number of seconds since January 1, 1970, Greenwich Mean Time (GMT).	GET_FORMAT( ) This MySQL function returns the format for a given data type, based on the standard given as the second argument. The format codes returned are the same codes used by the DATE_FORMAT() function.
HOUR( ) This MySQL function returns the hour for a DATETIMEor TIME column.	LAST_DAY( ) This MySQL function returns the date of the last day of the month for a given date or datetime value.
LOCALTIME( ) This MySQL function returns the current system date in yyyy-mm-dd hh:mm:ss format. It's synonymous with LOCALTIMESTAMP( ) and NOW( ).	LOCALTIMESTAMP( ) This MySQL function is synonymous with LOCALTIME( ) and NOW( ).
MAKEDATE( ) This MySQL function determines the date requested from the start of the given year, by adding the number of days given.	MAKETIME( ) This MySQL function converts a given hour, minute, and second to hh:mm:ss format.
MICROSECOND( ) This MySQL function extracts the microseconds value of a given time.	MINUTE( ) This MySQL function returns the minute value (0-59) of a given time.
MONTH( ) This MySQL function returns the numeric value of the month (0-12) for the date provided.	MONTHNAME( ) This MySQL function returns the name of the month for the date provided.
NOW( ) This MySQL function returns the current date and time. The format returned is yyyy-mm-dd hh:mm:ss.nnnnnn. It's synonymous with LOCALTIME( ) and LOCALTIMESTAMP( ).	PERIOD_ADD( ) This MySQL function adds a specified number of months to a period, which is a string containing only the year and month in either yyyymm or yymm format.
PERIOD_DIFF( ) This MySQL function returns the number of months between periods given.	QUARTER( ) This MySQL function returns the number of the quarter (1-4) for the date provided. The first quarter (i.e., three months) of each year has a value of 1.
SECOND( ) This MySQL function returns the seconds value (0-59) for a given time.	SEC_TO_TIME( ) This MySQL function returns the period for a given number of seconds in the format hh:mm:ss.
SLEEP( ) This MySQL function pauses the execution of an SQL statement in which it is given, for the number of seconds given.	STR_TO_DATE( ) This MySQL function returns the date and time of a given string for a given format.
SUBDATE( ) Use this MySQL function to subtract a date or time interval from the results of a DATE or TIME data type column. It's an alias for DATE_SUB( ).	SUBTIME( ) This MySQL function returns the date and time for the given string or column, decreased by the time given as the second argument (d hh:mm:ss).
SYSDATE( ) This MySQL function returns the system date in the yyyy-mm-dd hh:mm:ss format at the time it's executed.	TIME( ) This MySQL function returns the time from a given string or column containing date and time data.
TIMEDIFF( ) This MySQL function returns the time difference between the two times given.	TIMESTAMP( ) This MySQL function merges the date and time from given strings or columns that contain date and time data separately; the result is returned in yyyy-mm-dd hh:mm:ss format.
TIMESTAMPADD( ) This MySQL function adds the given number of intervals of time to the given date or time.	TIMESTAMPDIFF( ) This MySQL function returns the time difference between the two times given, but only for the interval being compared.
TIME_FORMAT( ) This MySQL function returns the time value of the time element provided and formats it according to formatting codes given.	TIME_TO_SEC( ) This MySQL function returns the number of seconds that the given time represents.
TO_DAYS( ) This MySQL function returns the date based on the number of days given, which are from the beginning of the currently used standard calendar.	UNIX_TIMESTAMP( ) This MySQL function returns the number of seconds since the start of the Unix epoch (January 1, 1970, Greenwich Mean Time).
UTC_DATE( ) This MySQL function returns the current Universal Time, Coordinated (UTC) date in yyyy-mm-dd format.	UTC_TIME( ) This MySQL function returns the current Universal Time, Coordinated (UTC) time in hh:mm:ss format.
UTC_TIMESTAMP( ) This MySQL function returns the current UTC date and time in yyyy-mm-dd hh:mm:ss format.	WEEK( ) This MySQL function returns the number of the week starting from the beginning of the year for the date provided.
WEEKDAY( ) This MySQL function returns the number for the day of the week. Monday is considered the first day of the week.	WEEKOFYEAR( ) This MySQL function returns the calendar week of the year for a given date. It's a bit synonymous withWEEK( ).
YEAR( ) This MySQL function returns the year of the date provided.	YEARWEEK( ) This MySQL function returns the year coupled with the number of the week into the year: yyyyww. By default, the first day of the week is Sunday and the basis of the calculation. This MySQL function is somewhat synonymous with WEEK( ).

Resource http://mysqlresources.com/documentation/date-time

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