15.00 - DisplacementOnOverlap - Teradata Database

Teradata Database Utilities

Product
Teradata Database
Release Number
15.00
Content Type
Configuration
Publication ID
B035-1102-015K
Language
English (United States)
Last Update
2018-09-25

DisplacementOnOverlap

Purpose  

Determines whether values that represent times during the closing hour of Daylight Savings Time (DST), but that do not explicitly specify a time zone offset value, are interpreted by Teradata Database as DST or standard time.

Note: This field is effective only when time zone strings are in effect, and the value of “TimeDateWZControl” is set to 3.

Field Group

General

Valid Settings

 

Setting

Description

0

Teradata Database assumes standard time zone offset. This is the same as setting 1.

1

Teradata Database assumes standard time zone offset. This is the same as setting 0.

2

Teradata Database assumes DST time zone offset.

Default

0

Changes Take Effect

After the DBS Control Record has been written.

Scenarios Daylight Savings Time and the Ambiguous Hour

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 setting for 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.