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https://issues.apache.org/jira/browse/SPARK-26812?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-26812:
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Assignee: Apache Spark
> PushProjectionThroughUnion nullability issue
> --------------------------------------------
>
> Key: SPARK-26812
> URL: https://issues.apache.org/jira/browse/SPARK-26812
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 2.4.0
> Reporter: Bogdan Raducanu
> Assignee: Apache Spark
> Priority: Major
>
> Union output data types are the output data types of the first child.
> However the other union children may have different values nullability.
> This means that we can't always push down a project on the children.
> To reproduce
> {code}
> Seq(Map("foo" -> "bar")).toDF("a").write.saveAsTable("table1")
> sql("SELECT 1 AS b").write.saveAsTable("table2")
> sql("CREATE OR REPLACE VIEW test1 AS SELECT map() AS a FROM table2 UNION ALL
> SELECT a FROM table1")
> sql("select * from test1").show
> {code}
> This fails becaus the plan is no longer resolved.
> The plan is broken by the PushProjectionThroughUnion rule which pushed down a
> cast to map<string,string> with values nullability=true on a child with type
> map<string, string> with values nullability=false.
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