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https://issues.apache.org/jira/browse/SPARK-34283?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-34283:
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Assignee: (was: Apache Spark)
> Combines all adjacent 'Union' operators into a single 'Union' when using
> 'Dataset.union.distinct'
> -------------------------------------------------------------------------------------------------
>
> Key: SPARK-34283
> URL: https://issues.apache.org/jira/browse/SPARK-34283
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: Zhichao Zhang
> Priority: Major
> Attachments: image-2021-01-29-11-12-44-112.png,
> image-2021-01-29-11-13-42-055.png, image-2021-01-29-11-14-08-822.png,
> image-2021-01-29-11-14-42-700.png
>
>
> Problem:
> Currently when using 'Dataset.union.distinct' to union some datasets,
> Optimizer can't combine all adjacent 'Union' operators into a single 'Union',
> but it can handle this case when using sql.
> For example:
> !image-2021-01-29-11-12-44-112.png!
> The 'Physical Plan' is shown below:
> !image-2021-01-29-11-13-42-055.png!
> But using sql:
> !image-2021-01-29-11-14-08-822.png!
> The 'Physical Plan' is shown below:
> !image-2021-01-29-11-14-42-700.png!
>
> Root cause:
> When using 'Dataset.union.distinct', the operator is 'Deduplicate(Columns,
> Union)', but AstBuilder transform sql 'Union' to operator 'Distinct(Union)',
> the rule 'CombineUnions' in Optimizer only handle 'Distinct(Union)' operator
> not Deduplicate(Columns, Union)
>
>
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