pitrou commented on code in PR #48002: URL: https://github.com/apache/arrow/pull/48002#discussion_r2546556204
########## docs/source/format/CanonicalExtensions.rst: ########## @@ -544,6 +544,49 @@ Primitive Type Mappings | UUID extension type | UUID | +----------------------+------------------------+ +.. _timestamp_with_offset_extension: + +Timestamp With Offset +============= +This type represents a timestamp column that stores potentially different timezone offsets per value. The timestamp is stored in UTC alongside the original timezone offset in minutes. +This extension type is intended to be compatible with ANSI SQL's ``TIMESTAMP WITH TIME ZONE``, which is supported by multiple database engines. + +* Extension name: ``arrow.timestamp_with_offset``. + +* The storage type of the extension is a ``Struct`` with 2 fields, in order: + + * ``timestamp``: a preferably non-nullable ``Timestamp(time_unit, "UTC")``, where ``time_unit`` is any Arrow ``TimeUnit`` (s, ms, us or ns). + + * ``offset_minutes``: a preferably non-nullable signed 16-bit integer (``Int16``) representing the offset in minutes from the UTC timezone. Negative offsets represent time zones west of UTC, while positive offsets represent east. Offsets range from -779 (-12:59) to +780 (+13:00). + +* Extension type parameters: + + * ``time_unit``: the time-unit of each of the stored UTC timestamps. + +* Description of the serialization: + + Extension metadata is an empty string. + +.. note:: + + It is also *permissible* for the ``offset_minutes`` field to be dictionary-encoded or run-end-encoded. + +.. note:: + + It is also *permissible* for ``timestamp`` and ``offset_minutes`` to be nullable, but not recommended. + + If ``timestamp`` is nullable and a value is found to be null, then the whole ``TimestampWithOffset`` value should be interpreted as null. One way of achieving this is to drop ``timestamp``'s validity buffer (V1) and replace the top-level struct's validity buffer (V2) with the result of ``V1 AND V2``. + + If ``offset_minutes`` is nullable and a value is found to be null, then this value should be interpreted as if the offset value were were zero. + + It is *recommended* that implementations normalize this type's representation by dropping the inner validity buffers and applying the aforementioned transformations, only keeping the top-level struct's validity buffer. + +.. note:: Review Comment: This seems slightly out of scope. We don't have any similar wording for built-in Arrow types such as Timestamp. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
