[jira] [Resolved] (SPARK-26812) PushProjectionThroughUnion nullability issue

["Wenchen Fan (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-26812?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wenchen Fan resolved SPARK-26812.
---------------------------------
       Resolution: Fixed
    Fix Version/s: 3.0.0

Issue resolved by pull request 23726
[https://github.com/apache/spark/pull/23726]

> 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
>            Priority: Major
>             Fix For: 3.0.0
>
>
> 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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