Oracle® Database Globalization Support Guide 10g Release 2 (10.2) Part Number B14225-02 |
|
|
View PDF |
This chapter includes the following topics:
Businesses conduct transactions across time zones. Oracle's datetime and interval datatypes and time zone support make it possible to store consistent information about the time of events and transactions.
Note:
This chapter describes Oracle datetime and interval datatypes. It does not attempt to describe ANSI datatypes or other kinds of datatypes except when noted.The datetime datatypes are DATE
, TIMESTAMP
, TIMESTAMP WITH TIME ZONE,
and TIMESTAMP WITH LOCAL TIME ZONE
. Values of datetime datatypes are sometimes called datetimes.
The interval datatypes are INTERVAL YEAR TO MONTH
and INTERVAL DAY TO SECOND
. Values of interval datatypes are sometimes called intervals.
Both datetimes and intervals are made up of fields. The values of these fields determine the value of the datatype. The fields that apply to all Oracle datetime and interval datatypes are:
YEAR
MONTH
DAY
HOUR
MINUTE
SECOND
TIMESTAMP WITH TIME ZONE
also includes these fields:
TIMEZONE_HOUR
TIMEZONE_MINUTE
TIMEZONE_REGION
TIMEZONE_ABBR
TIMESTAMP WITH LOCAL TIME ZONE
does not store time zone information internally, but you can see local time zone information in SQL output if the TZH:TZM
or TZR
TZD
format elements are specified.
The following sections describe the datetime datatypes and interval datatypes in more detail:
See Also:
Oracle Database SQL Reference for the valid values of the datetime and interval fields. Oracle Database SQL Reference also contains information about format elements.This section includes the following topics:
The DATE
datatype stores date and time information. Although date and time information can be represented in both character and number datatypes, the DATE
datatype has special associated properties. For each DATE
value, Oracle stores the following information: century, year, month, date, hour, minute, and second.
You can specify a date value by:
Specifying the date value as a literal
Converting a character or numeric value to a date value with the TO_DATE
function
A date can be specified as an ANSI date literal or as an Oracle date value.
An ANSI date literal contains no time portion and must be specified in exactly the following format:
DATE 'YYYY-MM-DD'
The following is an example of an ANSI date literal:
DATE '1998-12-25'
Alternatively, you can specify an Oracle date value as shown in the following example:
TO_DATE('1998-DEC-25 17:30','YYYY-MON-DD HH24:MI','NLS_DATE_LANGUAGE=AMERICAN')
The default date format for an Oracle date value is derived from the NLS_DATE_FORMAT
and NLS_DATE_LANGUAGE
initialization parameters. The date format in the example includes a two-digit number for the day of the month, an abbreviation of the month name, the last two digits of the year, and a 24-hour time designation. The specification for NLS_DATE_LANGUAGE
is included because 'DEC'
is not a valid value for MON
in all locales.
Oracle automatically converts character values that are in the default date format into date values when they are used in date expressions.
If you specify a date value without a time component, then the default time is midnight. If you specify a date value without a date, then the default date is the first day of the current month.
Oracle DATE
columns always contain fields for both date and time. If your queries use a date format without a time portion, then you must ensure that the time fields in the DATE
column are set to midnight. You can use the TRUNC
(date) SQL function to ensure that the time fields are set to midnight, or you can make the query a test of greater than or less than (<
, <=
, >=
, or >)
instead of equality or inequality (=
or !=)
. Otherwise, Oracle may not return the query results you expect.
See Also:
Oracle Database SQL Reference for more information about the DATE
datatype
Oracle Database SQL Reference for more information about literals, format elements such as MM
, and the TO_DATE
function
The TIMESTAMP
datatype is an extension of the DATE
datatype. It stores year, month, day, hour, minute, and second values. It also stores fractional seconds, which are not stored by the DATE
datatype.
Specify the TIMESTAMP
datatype as follows:
TIMESTAMP [(fractional_seconds_precision)]
fractional_seconds_precision
is optional and specifies the number of digits in the fractional part of the SECOND
datetime field. It can be a number in the range 0 to 9. The default is 6.
For example, '26-JUN-02 09:39:16.78'
shows 16.78 seconds. The fractional seconds precision is 2 because there are 2 digits in '78
'.
You can specify the TIMESTAMP
literal in a format like the following:
TIMESTAMP 'YYYY-MM-DD HH24:MI:SS.FF'
Using the example format, specify TIMESTAMP
as a literal as follows:
TIMESTAMP '1997-01-31 09:26:50.12'
The value of NLS_TIMESTAMP_FORMAT
initialization parameter determines the timestamp format when a character string is converted to the TIMESTAMP
datatype. NLS_DATE_LANGUAGE
determines the language used for character data such as MON
.
See Also:
Oracle Database SQL Reference for more information about the TIMESTAMP
datatype
TIMESTAMP WITH TIME ZONE
is a variant of TIMESTAMP
that includes a time zone offset or time zone region name in its value. The time zone offset is the difference (in hours and minutes) between local time and UTC (Coordinated Universal Time, formerly Greenwich Mean Time). Specify the TIMESTAMP WITH TIME ZONE
datatype as follows:
TIMESTAMP [(fractional_seconds_precision)] WITH TIME ZONE
fractional_seconds_precision
is optional and specifies the number of digits in the fractional part of the SECOND
datetime field.
You can specify TIMESTAMP WITH TIME ZONE
as a literal as follows:
TIMESTAMP '1997-01-31 09:26:56.66 +02:00'
Two TIMESTAMP WITH TIME ZONE
values are considered identical if they represent the same instant in UTC, regardless of the TIME ZONE
offsets stored in the data. For example, the following expressions have the same value:
TIMESTAMP '1999-01-15 8:00:00 -8:00' TIMESTAMP '1999-01-15 11:00:00 -5:00'
You can replace the UTC offset with the TZR
(time zone region) format element. The following expression specifies US/Pacific
for the time zone region:
TIMESTAMP '1999-01-15 8:00:00 US/Pacific'
To eliminate the ambiguity of boundary cases when the time switches from Standard Time to Daylight Saving Time, use both the TZR
format element and the corresponding TZD
format element. The TZD
format element is an abbreviation of the time zone region with Daylight Saving Time information included. Examples are PST
for US/Pacific standard time and PDT
for US/Pacific daylight time. The following specification ensures that a Daylight Saving Time value is returned:
TIMESTAMP '1999-10-29 01:30:00 US/Pacific PDT'
If you do not add the TZD
format element, and the datetime value is ambiguous, then Oracle returns an error if you have the ERROR_ON_OVERLAP_TIME
session parameter set to TRUE
. If ERROR_ON_OVERLAP_TIME
is set to FALSE
(the default value), then Oracle interprets the ambiguous datetime as Standard Time.
The default date format for the TIMESTAMP WITH TIME ZONE
datatype is determined by the value of the NLS_TIMESTAMP_TZ_FORMAT
initialization parameter.
See Also:
Oracle Database SQL Reference for more information about the TIMESTAMP WITH TIME ZONE
datatype
"TIMESTAMP Datatype" for more information about fractional seconds precision
Oracle Database SQL Reference for more information about format elements
Oracle Database SQL Reference for more information about setting the ERROR_ON_OVERLAP_TIME
session parameter
TIMESTAMP WITH LOCAL TIME ZONE
is another variant of TIMESTAMP
. It differs from TIMESTAMP WITH TIME ZONE
as follows: data stored in the database is normalized to the database time zone, and the time zone offset is not stored as part of the column data. When users retrieve the data, Oracle returns it in the users' local session time zone. The time zone offset is the difference (in hours and minutes) between local time and UTC (Coordinated Universal Time, formerly Greenwich Mean Time).
Specify the TIMESTAMP WITH LOCAL TIME ZONE
datatype as follows:
TIMESTAMP [(fractional_seconds_precision)] WITH LOCAL TIME ZONE
fractional_seconds_precision
is optional and specifies the number of digits in the fractional part of the SECOND
datetime field.
There is no literal for TIMESTAMP WITH LOCAL TIME ZONE
, but TIMESTAMP
literals and TIMESTAMP WITH TIME ZONE
literals can be inserted into a TIMESTAMP WITH LOCAL TIME ZONE
column.
The default date format for TIMESTAMP WITH LOCAL TIME ZONE
is determined by the value of the NLS_TIMESTAMP_FORMAT
initialization parameter.
See Also:
Oracle Database SQL Reference for more information about the TIMESTAMP WITH LOCAL TIME ZONE
datatype
"TIMESTAMP Datatype" for more information about fractional seconds precision
You can insert values into a datetime column in the following ways:
Insert a character string whose format is based on the appropriate NLS format value
Insert a literal
Insert a literal for which implicit conversion is performed
Use the TO_TIMESTAMP
, TO_TIMESTAMP_TZ
, or TO_DATE
SQL function
The following examples show how to insert data into datetime datatypes.
Example 4-1 Inserting Data into a DATE Column
Set the date format.
SQL> ALTER SESSION SET NLS_DATE_FORMAT='DD-MON-YYYY HH24:MI:SS';
Create a table table_dt
with columns c_id
and c_dt
. The c_id
column is of NUMBER
datatype and helps to identify the method by which the data is entered. The c_dt
column is of DATE
datatype.
SQL> CREATE TABLE table_dt (c_id NUMBER, c_dt DATE);
Insert a date as a character string.
SQL> INSERT INTO table_dt VALUES(1, '01-JAN-2003');
Insert the same date as a DATE
literal.
SQL> INSERT INTO table_dt VALUES(2, DATE '2003-01-01');
Insert the date as a TIMESTAMP
literal. Oracle drops the time zone information.
SQL> INSERT INTO table_dt VALUES(3, TIMESTAMP '2003-01-01 00:00:00 US/Pacific');
Insert the date with the TO_DATE
function.
SQL> INSERT INTO table_dt VALUES(4, TO_DATE('01-JAN-2003', 'DD-MON-YYYY'));
Display the data.
SQL> SELECT * FROM table_dt; C_ID C_DT ---------- -------------------- 1 01-JAN-2003 00:00:00 2 01-JAN-2003 00:00:00 3 01-JAN-2003 00:00:00 4 01-JAN-2003 00:00:00
Example 4-2 Inserting Data into a TIMESTAMP Column
Set the timestamp format.
SQL> ALTER SESSION SET NLS_TIMESTAMP_FORMAT='DD-MON-YY HH:MI:SSXFF';
Create a table table_ts
with columns c_id
and c_ts
. The c_id
column is of NUMBER
datatype and helps to identify the method by which the data is entered. The c_ts
column is of TIMESTAMP
datatype.
SQL> CREATE TABLE table_ts(c_id NUMBER, c_ts TIMESTAMP);
Insert a date and time as a character string.
SQL> INSERT INTO table_ts VALUES(1, '01-JAN-2003 2:00:00');
Insert the same date and time as a TIMESTAMP
literal.
SQL> INSERT INTO table_ts VALUES(2, TIMESTAMP '2003-01-01 2:00:00');
Insert the same date and time as a TIMESTAMP WITH TIME ZONE
literal. Oracle converts it to a TIMESTAMP
value, which means that the time zone information is dropped.
SQL> INSERT INTO table_ts VALUES(3, TIMESTAMP '2003-01-01 2:00:00 -08:00');
Display the data.
SQL> SELECT * FROM table_ts; C_ID C_TS ---------- ----------------------------- 1 01-JAN-03 02:00:00.000000 AM 2 01-JAN-03 02:00:00.000000 AM 3 01-JAN-03 02:00:00.000000 AM
Note that the three methods result in the same value being stored.
Example 4-3 Inserting Data into the TIMESTAMP WITH TIME ZONE Datatype
Set the timestamp format.
SQL> ALTER SESSION SET NLS_TIMESTAMP_TZ_FORMAT='DD-MON-RR HH:MI:SSXFF AM TZR';
Set the time zone to '-07:00'
.
SQL> ALTER SESSION SET TIME_ZONE='-7:00';
Create a table table_tstz
with columns c_id
and c_tstz
. The c_id
column is of NUMBER
datatype and helps to identify the method by which the data is entered. The c_tstz
column is of TIMESTAMP WITH TIME ZONE
datatype.
SQL> CREATE TABLE table_tstz (c_id NUMBER, c_tstz TIMESTAMP WITH TIME ZONE);
Insert a date and time as a character string.
SQL> INSERT INTO table_tstz VALUES(1, '01-JAN-2003 2:00:00 AM -07:00');
Insert the same date and time as a TIMESTAMP
literal. Oracle converts it to a TIMESTAMP WITH TIME ZONE
literal, which means that the session time zone is appended to the TIMESTAMP
value.
SQL> INSERT INTO table_tstz VALUES(2, TIMESTAMP '2003-01-01 2:00:00');
Insert the same date and time as a TIMESTAMP WITH TIME ZONE
literal.
SQL> INSERT INTO table_tstz VALUES(3, TIMESTAMP '2003-01-01 2:00:00 -8:00');
Display the data.
SQL> SELECT * FROM table_tstz; C_ID C_TSTZ ---------- ------------------------------------ 1 01-JAN-03 02:00.00:000000 AM -07:00 2 01-JAN-03 02:00:00.000000 AM -07:00 3 01-JAN-03 02:00:00.000000 AM -08:00
Note that the time zone is different for method 3, because the time zone information was specified as part of the TIMESTAMP WITH TIME ZONE
literal.
Example 4-4 Inserting Data into the TIMESTAMP WITH LOCAL TIME ZONE Datatype
Consider data that is being entered in Denver, Colorado, U.S.A., whose time zone is UTC-7.
SQL> ALTER SESSION SET TIME_ZONE='-07:00';
Create a table table_tsltz
with columns c_id
and c_tsltz
. The c_id
column is of NUMBER
datatype and helps to identify the method by which the data is entered. The c_tsltz
column is of TIMESTAMP WITH LOCAL TIME ZONE
datatype.
SQL> CREATE TABLE table_tsltz (c_id NUMBER, c_tsltz TIMESTAMP WITH LOCAL TIME ZONE);
Insert a date and time as a character string.
SQL> INSERT INTO table_tsltz VALUES(1, '01-JAN-2003 2:00:00');
Insert the same data as a TIMESTAMP WITH LOCAL TIME ZONE
literal.
SQL> INSERT INTO table_tsltz VALUES(2, TIMESTAMP '2003-01-01 2:00:00');
Insert the same data as a TIMESTAMP WITH TIME ZONE
literal. Oracle converts the data to a TIMESTAMP WITH LOCAL TIME ZONE
value. This means the time zone that is entered (-08:00
) is converted to the session time zone value (-07:00
).
SQL> INSERT INTO table_tsltz VALUES(3, TIMESTAMP '2003-01-01 2:00:00 -08:00');
Display the data.
SQL> SELECT * FROM table_tsltz; C_ID C_TSLTZ ---------- ------------------------------------ 1 01-JAN-03 02.00.00.000000 AM 2 01-JAN-03 02.00.00.000000 AM 3 01-JAN-03 03.00.00.000000 AM
Note that the information that was entered as UTC-8 has been changed to the local time zone, changing the hour from 2
to 3
.
See Also:
"Datetime SQL Functions" for more information about theTO_TIMESTAMP
or TO_TIMESTAMP_TZ
SQL functionsUse the TIMESTAMP
datatype when you need a datetime value without locale information. For example, you can store information about the times when workers punch a timecard in and out of their assembly line workstations. The TIMESTAMP
datatype uses 7 or 11 bytes of storage.
Use the TIMESTAMP WITH TIME ZONE
datatype when the application is used across time zones. Consider a banking company with offices around the world. It records a deposit to an account at 11 a.m. in London and a withdrawal of the same amount from the account at 9 a.m. in New York. The money is in the account for three hours. Unless time zone information is stored with the account transactions, it appears that the account is overdrawn from 9 a.m. to 11 a.m.
The TIMESTAMP WITH TIME ZONE
datatype requires 13 bytes of storage, or two more bytes of storage than the TIMESTAMP
and TIMESTAMP WITH LOCAL TIME ZONE
datatypes because it stores time zone information. The time zone is stored as an offset from UTC or as a time zone region name. The data is available for display or calculations without additional processing. A TIMESTAMP WITH TIME ZONE
column cannot be used as a primary key. If an index is created on a TIMESTAMP WITH TIME ZONE
column, it becomes a function-based index.
The TIMESTAMP WITH LOCAL TIME ZONE
datatype stores the timestamp without time zone information. It normalizes the data to the database time zone every time the data is sent to and from a client. It requires 11 bytes of storage.
The TIMESTAMP WITH LOCAL TIME ZONE
datatype is appropriate when the original time zone is of no interest, but the relative times of events are important. Consider the transactions described in the previous banking example. Suppose the data is recorded using the TIMESTAMP WITH LOCAL TIME ZONE
datatype. If the database time zone of the bank is set to Asia/Hong_Kong
, then an employee in Hong Kong who displays the data would see that the deposit was made at 7 p.m. and the withdrawal was made at 10 p.m. If the same data is displayed in London, it would show that the deposit was made at 11 a.m. and the withdrawal was made at 2 p.m. The three-hour difference is preserved, but the time zone/region of the original transaction is not. Because of this, the actual time of the transaction can be interpreted differently depending on the time zone/region from which the information is retrieved. For example, in London, the transactions appear to be conducted within business hours, in Hong Kong, they do not.
Note that, because the original time zone region of the time data is not preserved in the TIMESTAMP
WITH
LOCAL
TIME
ZONE
data type, time data referring to times from regions such as Brazil and Israel, regions that update their Daylight Savings Transition dates frequently and at irregular periods, may be inaccurate. If time information from these regions is key to your application, you may wish to consider using one of the other datetime types.
Interval datatypes store time durations. They are used primarily with analytic functions. For example, you can use them to calculate a moving average of stock prices. You must use interval datatypes to determine the values that correspond to a particular percentile. You can also use interval datatypes to update historical tables.
This section includes the following topics:
Inserting Values into Interval Datatypes
See Also:
Oracle Data Warehousing Guide for more information about analytic functions, including moving averages and inverse percentilesINTERVAL YEAR TO MONTH
stores a period of time using the YEAR
and MONTH
datetime fields. Specify INTERVAL YEAR TO MONTH
as follows:
INTERVAL YEAR [(year_precision)] TO MONTH
year_precision
is the number of digits in the YEAR
datetime field. Accepted values are 0 to 9. The default value of year_precision
is 2.
Interval values can be specified as literals. There are many ways to specify interval literals.The following is one example of specifying an interval of 123 years and 2 months.The year precision is 3.
INTERVAL '123-2' YEAR(3) TO MONTH
See Also:
Oracle Database SQL Reference for more information about specifying interval literals with theINTERVAL YEAR TO MONTH
datatypeINTERVAL DAY TO SECOND
stores a period of time in terms of days, hours, minutes, and seconds. Specify this datatype as follows:
INTERVAL DAY [(day_precision)] TO SECOND [(fractional_seconds_precision)]
day_precision
is the number of digits in the DAY
datetime field. Accepted values are 0 to 9. The default is 2.
fractional_seconds_precision
is the number of digits in the fractional part of the SECOND
datetime field. Accepted values are 0 to 9. The default is 6.
The following is one example of specifying an interval of 4 days, 5 hours, 12 minutes, 10 seconds, and 222 thousandths of a second. The fractional second precision is 3.
INTERVAL '4 5:12:10.222' DAY TO SECOND(3)
Interval values can be specified as literals. There are many ways to specify interval literals.
See Also:
Oracle Database SQL Reference for more information about specifying interval literals with theINTERVAL DAY TO SECOND
datatypeYou can insert values into an interval column in the following ways:
Insert an interval as a literal. For example:
INSERT INTO table1 VALUES (INTERVAL '4-2' YEAR TO MONTH);
This statement inserts an interval of 4 years and 2 months.
Oracle recognizes literals for other ANSI interval types and converts the values to Oracle interval values.
Use the NUMTODSINTERVAL
, NUMTOYMINTERVAL
, TO_DSINTERVAL
, and TO_YMINTERVAL
SQL functions.
See Also:
"Datetime SQL Functions"This section includes the following topics:
You can perform arithmetic operations on date (DATE
), timestamp (TIMESTAMP
, TIMESTAMP WITH TIME ZONE
, and TIMESTAMP WITH LOCAL TIME ZONE
) and interval (INTERVAL DAY TO SECOND
and INTERVAL YEAR TO MONTH
) data. You can maintain the most precision in arithmetic operations by using a timestamp datatype with an interval datatype.
You can use NUMBER
constants in arithmetic operations on date and timestamp values. Oracle internally converts timestamp values to date values before doing arithmetic operations on them with NUMBER
constants. This means that information about fractional seconds is lost during operations that include both date and timestamp values. Oracle interprets NUMBER
constants in datetime and interval expressions as number of days.
Each DATE
value contains a time component. The result of many date operations includes a fraction. This fraction means a portion of one day. For example, 1.5 days is 36 hours. These fractions are also returned by Oracle built-in SQL functions for common operations on DATE
data. For example, the built-in MONTHS_BETWEEN
SQL function returns the number of months between two dates. The fractional portion of the result represents that portion of a 31-day month.
Oracle performs all timestamp arithmetic in UTC time. For TIMESTAMP WITH LOCAL TIME ZONE
data, Oracle converts the datetime value from the database time zone to UTC and converts back to the database time zone after performing the arithmetic. For TIMESTAMP WITH TIME ZONE
data, the datetime value is always in UTC, so no conversion is necessary.
See Also:
Oracle Database SQL Reference for detailed information about datetime and interval arithmetic operations
"Datetime SQL Functions" for information about which functions cause implicit conversion to DATE
When you compare date and timestamp values, Oracle converts the data to the more precise datatype before doing the comparison. For example, if you compare data of TIMESTAMP WITH TIME ZONE
datatype with data of TIMESTAMP
datatype, Oracle converts the TIMESTAMP
data to TIMESTAMP WITH TIME ZONE
, using the session time zone.
The order of precedence for converting date and timestamp data is as follows:
DATE
TIMESTAMP
TIMESTAMP WITH LOCAL TIME ZONE
TIMESTAMP WITH TIME ZONE
For any pair of datatypes, Oracle converts the datatype that has a smaller number in the preceding list to the datatype with the larger number.
If you want to do explicit conversion of datetime datatypes, use the CAST
SQL function. You can explicitly convert DATE
, TIMESTAMP
, TIMESTAMP WITH TIME ZONE
, and TIMESTAMP WITH LOCAL TIME ZONE
to another datatype in the list.
See Also:
Oracle Database SQL ReferenceDatetime functions operate on date (DATE
), timestamp (TIMESTAMP
, TIMESTAMP WITH TIME ZONE
, and TIMESTAMP WITH LOCAL TIME ZONE
) and interval (INTERVAL DAY TO SECOND
, INTERVAL YEAR TO MONTH
) values.
Some of the datetime functions were designed for the Oracle DATE
datatype. If you provide a timestamp value as their argument, then Oracle internally converts the input type to a DATE
value. Oracle does not perform internal conversion for the ROUND
and TRUNC
functions.
Table 4-1 shows the datetime functions that were designed for the Oracle DATE
datatype. It contains cross-references to more detailed descriptions of the functions.
Table 4-1 Datetime Functions Designed for the DATE Datatype
Function | Description |
---|---|
Returns the last day of the month that contains |
|
Returns the number of months between |
|
Returns the date and time in Note: This function takes as input only a limited number of time zones. You can have access to a much greater number of time zones by combining the |
|
Returns the date of the first weekday named by |
|
|
Returns |
Returns |
Table 4-2 describes additional datetime functions and contains cross-references to more detailed descriptions.
Table 4-2 Additional Datetime Functions
Datetime Function | Description |
---|---|
Returns the current date in the session time zone in a value in the Gregorian calendar, of the |
|
Returns the current date and time in the session time zone as a |
|
Returns the value of the database time zone. The value is a time zone offset or a time zone region name |
|
Extracts and returns the value of a specified datetime field from a datetime or interval value expression |
|
Converts a |
|
Returns the current date and time in the session time zone in a value of the |
|
Converts number |
|
Converts number |
|
Returns the value of the current session's time zone |
|
Extracts the UTC from a datetime with time zone offset |
|
Returns the date and time of the operating system on which the database resides, taking into account the time zone of the database server's operating system that was in effect when the database was started |
|
Returns the system date, including fractional seconds and time zone of the system on which the database resides |
|
Converts a datetime or interval value of |
|
Converts a character string of |
|
Converts a datetime or interval value of |
|
Converts a character string of |
|
Converts a character string of |
|
Converts a character string of |
|
Returns the time zone offset that corresponds to the entered value, based on the date that the statement is executed |
See Also:
Oracle Database SQL ReferenceThis section includes the following topics:
Table 4-3 contains the names and descriptions of the datetime format parameters.
Table 4-3 Datetime Format Parameters
Their default values are derived from NLS_TERRITORY
.
You can specify their values by setting them in the initialization parameter file. You can specify their values for a client as client environment variables.
You can also change their values by changing their value in the initialization parameter file and then restarting the instance.
To change their values during a session, use the ALTER SESSION
statement.
See Also:
"Date and Time Parameters" for more information, including examples
The time zone environment variables are:
ORA_TZFILE
, which specifies the Oracle time zone file used by the database
ORA_SDTZ
, which specifies the default session time zone
ERROR_ON_OVERLAP_TIME
is a session parameter that determines how Oracle handles an ambiguous datetime boundary value. Ambiguous datetime values can occur when the time changes between Daylight Saving Time and standard time.
The possible values are TRUE
and FALSE
. When ERROR_ON_OVERLAP_TIME
is TRUE
, then an error is returned when Oracle encounters an ambiguous datetime value. When ERROR_ON_OVERLAP_TIME
is FALSE
, then ambiguous datetime values are assumed to be the standard time representation for the region. The default value is FALSE
.
See Also:
"Support for Daylight Saving Time"The Oracle time zone files contain the valid time zone names. The following information is also included for each time zone:
Offset from Coordinated Universal Time (UTC)
Transition times for Daylight Saving Time
Abbreviations for standard time and Daylight Saving Time
Two time zone files are included in the Oracle home directory. The default time zone file is $ORACLE_HOME/oracore/zoneinfo/timezonelrg.dat
, which contains all the time zones defined in the database. $ORACLE_HOME/oracore/zoneinfo/timezone.dat
contains only the most commonly used time zones.
If you use the larger time zone file, then you must continue to use it unless you are sure that none of the additional time zones that it contains are used for data that is stored in the database. Also, all databases and client installations that share information must use the same time zone file.
To enable the use of $ORACLE_HOME/oracore/zoneinfo/timezone.dat
, or if you are already using it as your time zone file and you want to continue to do so in an Oracle Database 10g environment, perform the following steps:
Shut down the database if it has been started.
Set the ORA_TZFILE
environment variable to $ORACLE_HOME/oracore/zoneinfo/timezone.dat
.
Restart the database.
Note:
If you are already using the default time zone file, then it is not practical to change to the smaller time zone file because the database may contain data with time zones that are not part of the smaller time zone file.Oracle's time zone data is derived from the public domain information available at ftp://elsie.nci.nih.gov/pub/
. Oracle's time zone data may not reflect the most recent data available at this site.
You can obtain a list of time zone names and time zone abbreviations from the time zone file that is installed with your database by entering the following statement:
SELECT tzname, tzabbrev FROM V$TIMEZONE_NAMES;
For the default time zone file, this statement results in output similar to the following:
TZNAME TZABBREV -------------------- ---------- Africa/Algiers LMT Africa/Algiers PMT Africa/Algiers WET Africa/Algiers WEST Africa/Algiers CET Africa/Algiers CEST Africa/Cairo LMT Africa/Cairo EET Africa/Cairo EEST Africa/Casablanca LMT Africa/Casablanca WET Africa/Casablanca WEST Africa/Casablanca CET ... W-SU LMT W-SU MMT W-SU MST W-SU MDST W-SU S W-SU MSD W-SU MSK W-SU EET W-SU EEST WET LMT WET WEST WET WET 1393 rows selected.
There are 6 time zone abbreviations associated with the Africa/Algiers time zone, 3 abbreviations associated with the Africa/Cairo time zone, and 4 abbreviations associated with the Africa/Casablanca time zone. The following table shows the time zone abbreviations and their meanings.
Time Zone Abbreviation | Meaning |
---|---|
LMT | Local Mean Time |
PMT | Paris Mean Time |
WET | Western European Time |
WEST | Western European Summer Time |
CET | Central Europe Time |
CEST | Central Europe Summer Time |
EET | Eastern Europe Time |
EEST | Eastern Europe Summer Time |
Note that an abbreviation can be associated with more than one time zone. For example, CET is associated with both Africa/Algiers and Africa/Casablanca, as well as time zones in Europe.
If you want a list of time zones without repeating the time zone name for each abbreviation, use the following query:
SELECT UNIQUE tzname FROM V$TIMEZONE_NAMES;
For the default time zone file, this results in output similar to the following:
TZNAME -------------------- Africa/Algiers Africa/Cairo Africa/Casablanca Africa/Ceuta ... US/Pacific US/Pacific-New US/Samoa UTC W-SU WET
The default time zone file contains more than 350 unique time zone names. The small time zone file contains more than 180 unique time zone names.
See Also:
"Time Zone Names" for a list of valid Oracle time zone names
The time zone files that are supplied with Oracle Database 10g have been updated from version 1 to version 2 to reflect changes in transition rules for some time zone regions. The changes may affect existing data of TIMESTAMP WITH TIME ZONE
datatype. For example, when users enter TIMESTAMP '2003-02-17 09:00 America/Sao_Paulo'
, Oracle converts the data to UTC based on the transition rules in the time zone file and stores the data on disk. When the version 1 transition rules were in effect, Oracle stored '2003-02-17 11:00:00'
and the time zone ID for 'America/Sao_Paulo'
because the offset in this example was '-02:00'
. The offset under version 2 transition rules is '-03:00'
. When users retrieve the data, they receive '2003-02-17 08:00:00 American/Sao_Paulo'
. There is a one-hour difference compared to the original data.
You can use the $ORACLE_HOME/rdbms/admin/utltzuv2.sql
script to discover all columns of TIMESTAMP WITH TIME ZONE
datatype in your database. Execute the script before you update the database time zone file to version 2. The result is stored in the sys.sys_tzuv2_temptab
table. The table has 5 columns: table_owner
, table_name
, column_name
, rowcount
, nested_tab
. The nested_tab
column indicates whether the table mentioned in the table_name
column is a nested table.
If your database has data that will be affected by the time zone file update, then back up the data before you upgrade the time zone file to version 2. After the upgrade, you must update the data to ensure that the data is stored based on the new rules. For example, if user scott
has a table tztab
, as in the following:
CREATE TABLE tztab(x NUMBER PRIMARY KEY, y TIMESTAMP WITH TIME ZONE); INSERT INTO tztab VALUES(1, timestamp '2003-02-17 09:00:00 America/Sao_Paulo');
Before upgrading, you can create a table tztab_back
(note that column y
here is defined as VARCHAR2
to preserve the original value):
CREATE TABLE tztab_back(x NUMBER PRIMARY KEY, y VARCHAR2(256)); INSERT INTO tztab_back SELECT x, TO_CHAR(y, 'YYYY-MM-DD HH24.MI.SSXFF TZR') FROM tztab;
After upgrading, you need to update the data in the table tztab
using the value in tztab_back
, as in the following:
UPDATE tztab t SET t.y = (SELECT to_timestamp_tz(t1.y,'YYYY-MM-DD HH24.MI.SSXFF TZR') FROM tztab_back t1 WHERE t.x=t1.x);
Or you can use the Export utility to export your data before the upgrade and then import your data again after the upgrade. See the comments in the utltzuv2.sql
script for more information.
Although the transition rule changes may affect data of TIMESTAMP WITH LOCAL TIME ZONE
datatype, there is no way to upgrade the data. The data cannot be upgraded because this type does not preserve the original time zone/region associated with the data.
Time zone regions in Brazil and Israel may have frequent transition rules changes, perhaps as often as every year. Use the time zone offset instead of the time zone region name to avoid storing inconsistent data.
Customers using time zone regions that have been updated in version 2 of the time zone files are required to update all Oracle9i Database clients and databases that will communicate with an Oracle Database 10g server. This ensures that all environments will have the same version of the time zone file, version 2. This is not a requirement for other customers, but Oracle still recommends that you do so. Users who need to update their time zone files to version 2 can find the following information on OracleMetaLink (http://metalink.oracle.com
):
readme.txt
contains the list of time zone regions that have changed from version 1 to version 2.
Actual time zone files for version 2 for the Oracle9i Database release.
utltzuv2.sql
script that must be run on the server side to find out if the database already has a column of type TIMESTAMP
WITH
TIME
ZONE
. It contains time zones that have changed from version 1 to version 2.
Oracle Database 10g clients that communicate with Oracle Database 10g servers automatically get version 2 of the time zone file, so there is no need to download the new time zone file.
See Also:
$ORACLE_HOME/oracore/zoneinfo/readme.txt
for detailed information about time zone file updates
Oracle Database Upgrade Guide for upgrade information
Set the database time zone when the database is created by using the SET TIME_ZONE
clause of the CREATE DATABASE
statement. If you do not set the database time zone, then it defaults to the time zone of the server's operating system.
The time zone may be set to an absolute offset from UTC or to a named region. For example, to set the time zone to an offset from UTC, use a statement similar to the following:
CREATE DATABASE db01 ... SET TIME_ZONE='-05:00';
The range of valid offsets is -12:00 to +14:00.
To set the time zone to a named region, use a statement similar to the following:
CREATE DATABASE db01 ... SET TIME_ZONE='Europe/London';
Note:
The database time zone is relevant only forTIMESTAMP WITH LOCAL TIME ZONE
columns. Oracle Corporation recommends that you set the database time zone to UTC (0:00) to avoid data conversion and improve performance when data is transferred among databases. This is especially important for distributed databases, replication, and exporting and importing.You can change the database time zone by using the SET TIME_ZONE
clause of the ALTER DATABASE
statement. For example:
ALTER DATABASE SET TIME_ZONE='05:00'; ALTER DATABASE SET TIME_ZONE='Europe/London';
The ALTER DATABASE SET TIME_ZONE
statement returns an error if the database contains a table with a TIMESTAMP WITH LOCAL TIME ZONE
column and the column contains data.
The change does not take effect until the database has been shut down and restarted.
You can find out the database time zone by entering the following query:
SELECT dbtimezone FROM DUAL;
You can set the default session time zone with the ORA_SDTZ
environment variable. When users retrieve TIMESTAMP WITH LOCAL TIME ZONE
data, Oracle returns it in the users' session time zone. The session time zone also takes effect when a TIMESTAMP
value is converted to the TIMESTAMP WITH TIME ZONE
or TIMESTAMP WITH LOCAL TIME ZONE
datatype.
Note:
Setting the session time zone does not affect the value returned by theSYSDATE
and SYSTIMESTAMP
SQL function. SYSDATE
returns the date and time of the operating system on which the database resides, taking into account the time zone of the database server's operating system that was in effect when the database was started.The ORA_SDTZ
environment variable can be set to the following values:
Absolute offset from UTC (for example, '-05:00'
)
Time zone region name (for example, 'Europe/London'
)
To set ORA_SDTZ
, use statements similar to one of the following in a UNIX environment (C shell):
% setenv ORA_SDTZ 'OS_TZ' % setenv ORA_SDTZ 'DB_TZ' % setenv ORA_SDTZ '-05:00' % setenv ORA_SDTZ 'Europe/London'
You can change the time zone for a specific SQL session with the SET TIME_ZONE
clause of the ALTER SESSION
statement.
TIME_ZONE
can be set to the following values:
Default local time zone when the session was started (local
)
Database time zone (dbtimezone
)
Absolute offset from UTC (for example, '+10:00'
)
Time zone region name (for example, 'Asia/Hong_Kong'
)
Use ALTER SESSION
statements similar to the following:
ALTER SESSION SET TIME_ZONE=local; ALTER SESSION SET TIME_ZONE=dbtimezone; ALTER SESSION SET TIME_ZONE='+10:00'; ALTER SESSION SET TIME_ZONE='Asia/Hong_Kong';
You can find out the current session time zone by entering the following query:
SELECT sessiontimezone FROM DUAL;
A datetime SQL expression can be one of the following:
A datetime column
A compound expression that yields a datetime value
A datetime expression can include an AT LOCAL
clause or an AT TIME ZONE
clause. If you include an AT LOCAL
clause, then the result is returned in the current session time zone. If you include the AT TIME ZONE
clause, then use one of the following settings with the clause:
Time zone offset: The string '(+|-)HH:MM'
specifies a time zone as an offset from UTC. For example, '-07:00'
specifies the time zone that is 7 hours behind UTC. For example, if the UTC time is 11:00 a.m., then the time in the '-07:00'
time zone is 4:00 a.m.
DBTIMEZONE
: Oracle uses the database time zone established (explicitly or by default) during database creation.
SESSIONTIMEZONE
: Oracle uses the session time zone established by default or in the most recent ALTER SESSION
statement.
Time zone region name: Oracle returns the value in the time zone indicated by the time zone region name. For example, you can specify Asia/Hong_Kong
.
An expression: If an expression returns a character string with a valid time zone format, then Oracle returns the input in that time zone. Otherwise, Oracle returns an error.
The following example converts the datetime value in the America/New_York
time zone to the datetime value in the America/Los_Angeles
time zone.
Example 4-5 Converting a Datetime Value to Another Time Zone
SELECT FROM_TZ(CAST(TO_DATE('1999-12-01 11:00:00', 'YYYY-MM-DD HH:MI:SS') AS TIMESTAMP), 'America/New_York') AT TIME ZONE 'America/Los_Angeles' "West Coast Time" FROM DUAL; West Coast Time ---------------------------------------------------------- 01-DEC-99 08.00.00.000000 AM AMERICA/LOS_ANGELES
See Also:
Oracle Database SQL ReferenceOracle automatically determines whether Daylight Saving Time is in effect for a specified time zone and returns the corresponding local time. The datetime value is usually sufficient for Oracle to determine whether Daylight Saving Time is in effect for a specified time zone. The periods when Daylight Saving Time begins or ends are boundary cases. For example, in the Eastern region of the United States, the time changes from 01:59:59 a.m. to 3:00:00 a.m. when Daylight Saving Time goes into effect. The interval between 02:00:00 and 02:59:59 a.m. does not exist. Values in that interval are invalid. When Daylight Saving Time ends, the time changes from 02:00:00 a.m. to 01:00:01 a.m. The interval between 01:00:01 and 02:00:00 a.m. is repeated. Values from that interval are ambiguous because they occur twice.
To resolve these boundary cases, Oracle uses the TZR
and TZD
format elements. TZR
represents the time zone region in datetime input strings. Examples are 'Australia/North
', 'UTC
', and 'Singapore
'. TZD
represents an abbreviated form of the time zone region with Daylight Saving Time information. Examples are 'PST
' for US/Pacific standard time and 'PDT
' for US/Pacific daylight time. To see a list of valid values for the TZR
and TZD
format elements, query the TZNAME
and TZABBREV
columns of the V$TIMEZONE_NAMES
dynamic performance view.
See Also:
"Time Zone Names" for a list of valid time zonesThe TIMESTAMP
datatype does not accept time zone values and does not calculate Daylight Saving Time.
The TIMESTAMP WITH TIME ZONE
and TIMESTAMP WITH LOCAL TIME ZONE
datatypes have the following behavior:
If a time zone region is associated with the datetime value, then the database server knows the Daylight Saving Time rules for the region and uses the rules in calculations.
Daylight Saving Time is not calculated for regions that do not use Daylight Saving Time.
The rest of this section contains examples that use datetime datatypes. The examples use the global_orders
table. It contains the orderdate1
column of TIMESTAMP
datatype and the orderdate2
column of TIMESTAMP WITH TIME ZONE
datatype. The global_orders
table is created as follows:
CREATE TABLE global_orders ( orderdate1 TIMESTAMP(0), orderdate2 TIMESTAMP(0) WITH TIME ZONE); INSERT INTO global_orders VALUES ( '28-OCT-00 11:24:54 PM', '28-OCT-00 11:24:54 PM America/New_York');
Example 4-6 Comparing Daylight Saving Time Calculations Using TIMESTAMP WITH TIME ZONE and TIMESTAMP
SELECT orderdate1 + INTERVAL '8' HOUR, orderdate2 + INTERVAL '8' HOUR FROM global_orders;
The following output results:
ORDERDATE1+INTERVAL'8'HOUR ORDERDATE2+INTERVAL'8'HOUR -------------------------- -------------------------- 29-OCT-00 07.24.54.000000 AM 29-OCT-00 06.24.54.000000 AM AMERICA/NEW_YORK
This example shows the effect of adding 8 hours to the columns. The time period includes a Daylight Saving Time boundary (a change from Daylight Saving Time to standard time). The orderdate1
column is of TIMESTAMP
datatype, which does not use Daylight Saving Time information and thus does not adjust for the change that took place in the 8-hour interval. The TIMESTAMP WITH TIME ZONE
datatype does adjust for the change, so the orderdate2
column shows the time as one hour earlier than the time shown in the orderdate1
column.
Note:
If you have created aglobal_orders
table for the previous examples, then drop the global_orders
table before you try Example 4-7 through Example 4-8.Example 4-7 Comparing Daylight Saving Time Calculations Using TIMESTAMP WITH LOCAL TIME ZONE and TIMESTAMP
The TIMESTAMP WITH LOCAL TIME ZONE
datatype uses the value of TIME_ZONE
that is set for the session environment. The following statements set the value of the TIME_ZONE
session parameter and create a global_orders
table. The global_orders
table has one column of TIMESTAMP
datatype and one column of TIMESTAMP WITH LOCAL TIME ZONE
datatype.
ALTER SESSION SET TIME_ZONE='America/New_York'; CREATE TABLE global_orders ( orderdate1 TIMESTAMP(0), orderdate2 TIMESTAMP(0) WITH LOCAL TIME ZONE ); INSERT INTO global_orders VALUES ( '28-OCT-00 11:24:54 PM', '28-OCT-00 11:24:54 PM' );
Add 8 hours to both columns.
SELECT orderdate1 + INTERVAL '8' HOUR, orderdate2 + INTERVAL '8' HOUR FROM global_orders;
Because a time zone region is associated with the datetime value for orderdate2
, the Oracle server uses the Daylight Saving Time rules for the region. Thus the output is the same as in Example 4-6. There is a one-hour difference between the two calculations because Daylight Saving Time is not calculated for the TIMESTAMP
datatype, and the calculation crosses a Daylight Saving Time boundary.
Example 4-8 Daylight Saving Time Is Not Calculated for Regions That Do Not Use Daylight Saving Time
Set the time zone region to UTC. UTC does not use Daylight Saving Time.
ALTER SESSION SET TIME_ZONE='UTC';
Truncate the global_orders
table.
TRUNCATE TABLE global_orders;
Insert values into the global_orders
table.
INSERT INTO global_orders VALUES ( '28-OCT-00 11:24:54 PM', TIMESTAMP '2000-10-28 23:24:54 ' );
Add 8 hours to the columns.
SELECT orderdate1 + INTERVAL '8' HOUR, orderdate2 + INTERVAL '8' HOUR FROM global_orders;
The following output results.
ORDERDATE1+INTERVAL'8'HOUR ORDERDATE2+INTERVAL'8'HOUR -------------------------- --------------------------- 29-OCT-00 07.24.54.000000000 AM 29-OCT-00 07.24.54.000000000 AM UTC
The times are the same because Daylight Saving Time is not calculated for the UTC time zone region.