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https://issues.apache.org/jira/browse/SPARK-25278?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Wenchen Fan resolved SPARK-25278.
---------------------------------
Resolution: Fixed
Fix Version/s: 2.4.0
Issue resolved by pull request 22284
[https://github.com/apache/spark/pull/22284]
> Number of output rows metric of union of views is multiplied by their
> occurrences
> ---------------------------------------------------------------------------------
>
> Key: SPARK-25278
> URL: https://issues.apache.org/jira/browse/SPARK-25278
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.3.1
> Reporter: Jacek Laskowski
> Priority: Major
> Fix For: 2.4.0
>
> Attachments: union-2-views.png, union-3-views.png
>
>
> When you use a view in a union multiple times (self-union), the {{number of
> output rows}} metric seems to be the correct {{number of output rows}}
> multiplied by the occurrences of the view, e.g.
> {code:java}
> scala> spark.version
> res0: String = 2.3.1
> val name = "demo_view"
> sql(s"CREATE OR REPLACE VIEW $name AS VALUES 1,2")
> assert(spark.catalog.tableExists(name))
> val view = spark.table(name)
> assert(view.count == 2)
> view.union(view).show // gives 4 for every view (as a LocalTableScan), but
> should be 2
> view.union(view).union(view).show // gives 6{code}
> I think it's because {{View}} logical operator is a {{MultiInstanceRelation}}
> (and think other {{MultiInstanceRelations}} may also be affected).
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