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https://issues.apache.org/jira/browse/IMPALA-2272?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Csaba Ringhofer resolved IMPALA-2272.
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Fix Version/s: Impala 4.1.0
Resolution: Fixed
Resolved by IMPALA-9498
> Parquet scanner always materializes NULL for empty collections
> --------------------------------------------------------------
>
> Key: IMPALA-2272
> URL: https://issues.apache.org/jira/browse/IMPALA-2272
> Project: IMPALA
> Issue Type: Bug
> Components: Backend
> Affects Versions: Impala 2.3.0
> Reporter: Skye Wanderman-Milne
> Priority: Minor
> Labels: complextype, nested_types
> Fix For: Impala 4.1.0
>
>
> Currently the Parquet scanner will always materialize a NULL slot for an
> empty collection, rather than an empty ArrayValue/CollectionValue. It is not
> currently possible to write a query that exposes this bug (i.e. it's not
> possible to write a query that distinguishes between an empty and NULL
> collection), but it will be once we add expressions that take collections as
> input (e.g. "select array_column is null from tbl").
> We have this bug because the parquet scanner only looks at the repeated field
> of an array, not the containing group field. To fix it, it will have to
> consider the def/rep levels of both.
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