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https://issues.apache.org/jira/browse/CALCITE-5155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17603267#comment-17603267
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Julian Hyde commented on CALCITE-5155:
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Yes, offsets are definitely required, but I was thinking to make the offset
part of the definition of the time unit. For example the regular 'week' unit
would be defined such that it starts a cycle on 1900/01/01 (which happens to be
a Monday). If your week starts on Sunday you should define a 'genesis week'
time unit that starts on say 1900/01/06 (which is a Sunday).
Similarly, each installation could define their own financial year with its own
offset.
Most time units (e.g. minutes) use '1970/01/01 00:00:00' as their offset and/or
align with their parent time unit.
> Extensible time units
> ---------------------
>
> Key: CALCITE-5155
> URL: https://issues.apache.org/jira/browse/CALCITE-5155
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Priority: Major
>
> Allow a type system to define its own time units and how they are rolled up.
> Currently, time units are used in the {{EXTRACT}}, {{FLOOR}}, {{TRUNC}}
> functions, and include {{YEAR}}, {{QUARTER}}, {{MONTH}}, {{HOUR}},
> {{MINUTE}}, {{NANOSECOND}}. For example {{FLOOR(t TO HOUR)}} is valid.
> A type system would be allowed to define extra time units. Once a time unit
> is defined the {{EXTRACT}}, {{FLOOR}} and {{TRUNC}} functions should just
> work.
> The definition of might consist of a base unit and multiplier. So
> {{MINUTE15}} would be based on {{MINUTE}} with a multiplier of 15.
> Various rules know that you can roll up {{FLOOR(t TO DAY)}} to {{FLOOR(t TO
> MONTH)}} but you cannot roll {{FLOOR(t TO WEEK)}} to {{FLOOR(t TO MONTH)}}.
> When you define a new time unit, the type system can deduce that full set of
> time units that it can roll up to, and which can roll up to it.
> Should we support time units that do not evenly divide the next largest time
> unit? For example the number of seconds since the top of the hour modulo 7.
> 60 and 3,600 are not a multiples of 7, so {{SecondOfHourMod7}} would be
> different from {{SecondOfMinuteMod7}}.
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