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https://issues.apache.org/jira/browse/PARQUET-1510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16752590#comment-16752590
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ASF GitHub Bot commented on PARQUET-1510:
-----------------------------------------
rdblue commented on pull request #603: PARQUET-1510: Fix notEq for optional
columns with null values.
URL: https://github.com/apache/parquet-mr/pull/603
Dictionaries cannot contain null values, so notEq filters cannot
conclude that a block cannot match using only the dictionary. Instead,
it must also check whether the block may have at least one null value.
If there are no null values, then the existing check is correct.
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> Dictionary filter skips null values when evaluating not-equals.
> ---------------------------------------------------------------
>
> Key: PARQUET-1510
> URL: https://issues.apache.org/jira/browse/PARQUET-1510
> Project: Parquet
> Issue Type: Improvement
> Reporter: Ryan Blue
> Priority: Major
> Labels: pull-request-available
>
> This was discovered in Spark, see SPARK-26677. From the Spark PR:
> {code}
> // Repeat the values to get dictionary encoding.
> Seq(Some("A"), Some("A"),
> None).toDF.repartition(1).write.mode("overwrite").parquet("/tmp/foo")
> spark.read.parquet("/tmp/foo").where("NOT (value <=> 'A')").show()
> +-----+
> |value|
> +-----+
> +-----+
> {code}
> {code}
> // Use plain encoding.
> Seq(Some("A"),
> None).toDF.repartition(1).write.mode("overwrite").parquet("/tmp/bar")
> spark.read.parquet("/tmp/bar").where("NOT (value <=> 'A')").show()
> +-----+
> |value|
> +-----+
> | null|
> +-----+
> {code}
> This is a correctness issue.
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