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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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Wenchen Fan resolved SPARK-34283.
---------------------------------
Fix Version/s: 3.2.0
Resolution: Fixed
Issue resolved by pull request 31404
[https://github.com/apache/spark/pull/31404]
> Combines all adjacent 'Union' operators into a single 'Union' when using
> 'Dataset.union.distinct.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
> Fix For: 3.2.0
>
> 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.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.union.distinct', the operator is
> 'Deduplicate(Keys, Union)', but AstBuilder transform sql 'Union' to operator
> 'Distinct(Union)', the rule 'CombineUnions' in Optimizer only handle
> 'Distinct(Union)' operator but not Deduplicate(Keys, Union).
>
>
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