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https://issues.apache.org/jira/browse/DRILL-3229?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14971766#comment-14971766
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Steven Phillips commented on DRILL-3229:
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Regarding the list writer, I know it is a bit confusing, so I will try to give
a better explanation for how it works. It confuses me at times as well.
The type promotion was designed with the possibility of allowing other
promotions in mind, but I am currently only doing promotion to Union. We should
have a discussion about what other promotions we want to allow.
Screen currently returns a Union type to the user. This is an area that will
require additional enhancement. The DrillClient has no problem dealing with a
Union vector. The jdbc driver, on the other hand, has only limited support for
a Union type, currently. I think we might need to add a feature similar to what
we have with complex types, which will determine if the client is able to
handle Union types, and convert to json if it doesn't. So metadata queries will
also return a Union type.
As for case statements, I am leaning more toward a general philosophy of trying
as much as we can to not fail queries, and so if there is something Drill can
do to execute a query, it should do that. So I am leaning toward option 3.
An untyped-null type is supported as part of a Union vector. This null value is
encoded in the 'type' vector. This patch does not introduce a standalone
Untyped Null Vector. That will be a separate patch.
I will update the design document with what I have said here.
> Create a new EmbeddedVector
> ---------------------------
>
> Key: DRILL-3229
> URL: https://issues.apache.org/jira/browse/DRILL-3229
> Project: Apache Drill
> Issue Type: Sub-task
> Components: Execution - Codegen, Execution - Data Types, Execution -
> Relational Operators, Functions - Drill
> Reporter: Jacques Nadeau
> Assignee: Hanifi Gunes
> Fix For: Future
>
>
> Embedded Vector will leverage a binary encoding for holding information about
> type for each individual field.
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