[jira] [Resolved] (SPARK-52462) Enforce type coercion before children output deduplication in Union

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

     [ https://issues.apache.org/jira/browse/SPARK-52462?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wenchen Fan resolved SPARK-52462.
---------------------------------
    Fix Version/s: 4.1.0
       Resolution: Fixed

Issue resolved by pull request 51172
[https://github.com/apache/spark/pull/51172]

> Enforce type coercion before children output deduplication in Union
> -------------------------------------------------------------------
>
>                 Key: SPARK-52462
>                 URL: https://issues.apache.org/jira/browse/SPARK-52462
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 4.1.0
>            Reporter: Mihailo Aleksic
>            Assignee: Mihailo Aleksic
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 4.1.0
>
>
> Right now, query the following query produces plans that are not consistent over different underlying table providers. Query:
> SELECT col1, col2, col3, NULLIF('','') AS col4
> FROM table
> UNION ALL
> SELECT col2, col2, null AS col3, col4
> FROM table;
> This happens because of rule ordering:
>  - Sometimes: ... -> WidenSetOperationTypes -> ... -> ResolveReferences (deduplication of Union children outputs) -> ...
>  - Sometimes: ... -> ResolveReferences (deduplication of Union children outputs) -> ... -> WidenSetOperationTypes -> ...
> In this issue I propose that we align those two by enforcing type coercion to happen before deduplication.



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