Changing Time Zone Strings and Rules - Teradata Database

Changing Time Zone Strings and Rules

Note: Teradata requests that customers open an incident so that the Customer Support Center can assist you in changing time zone settings on your system.

If you do not need Daylight Saving Time, you can set the time using the DBS Control utility settings SystemTimeZoneHour and SystemTimeZoneMinute.

To redefine your time zone, check the list of available time zone strings and their rules in
/usr/tdbms/etc/tdlocaledef_tzrules.txt. These rules are also in the GetTimeZoneDisplacement UDF. To change a time zone string and rules, you must change both the GetTimeZoneDisplacement UDF and tdlocaledef.

For more information, see “Adding or Modifying Time Zone Strings” under the topic “GetTimeZoneDisplacement” in SQL Functions, Operators, Expressions, and Predicates and DBS Control utility and Teradata Locale Definition utility in Utilities.

Locales that observe Daylight Savings Time (DST) set their clocks ahead one hour for a portion of the year for DST, then return their clocks to standard time by setting the clocks back. As a consequence, on the day when DST ends and clocks are turned back an hour, the times within this regained hour occur twice in the same day.

Without a way to distinguish the DST (first) occurrence of a specific time value within this hour from the standard time (second) occurrence, these time values are ambiguous unless a time zone offset is explicitly specified with the time value.

Teradata Database can automatically account for DST time switching through the use of time zone strings. Time zone strings allow you to define named time zones for locales based on their time offset from UTC. For locales that observe DST, time zone strings can include rules that define when DST starts and ends. Teradata Database uses this information to determine appropriate handling of time and date information, and to automatically adjust time zone offsets as appropriate for locales that observe DST.

However, when time zone strings are used for these locales, but time zone offset values are not included with time values, Teradata Database cannot determine whether time values within this ambiguous hour should be interpreted and treated as DST or as standard time. In these cases, the DBS Control setting for DisplacementOnOverlap determines whether these times are assumed by Teradata Database to have a DST or standard time zone offset.

Note: This issue occurs only when the following three conditions are true:

Time zone strings are used for DST locales

Time values do not include a time zone offset value

The DBS Control field TimeDateWZControl is set to 3 (date and time values without time zone offset information are stored using system local time)

For more information on...	See...
Time zone strings	Database Administration. SQL Functions, Operators, Expressions, and Predicates. the Teradata Locale Definition Utility chapter in Utilities.
DisplacementOnOverlap TimeDateWZControl	the DBS Control chapter in Utilities.