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https://issues.apache.org/jira/browse/SPARK-9740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14682405#comment-14682405
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Herman van Hovell commented on SPARK-9740:
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I think Hive uses a Flag, {{skipNulls}}, for this:
https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFFirstValue.java#L62
https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFLastValue.java#L52
It is not very well documented.
Hive defaults to including (respecting) nulls.
> first/last aggregate NULL behavior
> ----------------------------------
>
> Key: SPARK-9740
> URL: https://issues.apache.org/jira/browse/SPARK-9740
> Project: Spark
> Issue Type: Sub-task
> Components: SQL
> Reporter: Herman van Hovell
> Assignee: Yin Huai
>
> The FIRST/LAST aggregates implemented as part of the new UDAF interface,
> return the first or last non-null value (if any) found. This is a departure
> from the behavior of the old FIRST/LAST aggregates and from the
> FIRST_VALUE/LAST_VALUE aggregates in Hive. These would return a null value,
> if that happened to be the first/last value seen. SPARK-9592 tries to 'fix'
> this behavior for the old UDAF interface.
> Hive makes this behavior configurable, by adding a skipNulls flag. I would
> suggest to do the same, and make the default behavior compatible with Hive.
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