[jira] [Commented] (SPARK-21335) support un-aliased subquery

["Apache Spark (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-21335?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16524527#comment-16524527 ] 

Apache Spark commented on SPARK-21335:
--------------------------------------

User 'cnZach' has created a pull request for this issue:
https://github.com/apache/spark/pull/21647

> support un-aliased subquery
> ---------------------------
>
>                 Key: SPARK-21335
>                 URL: https://issues.apache.org/jira/browse/SPARK-21335
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Wenchen Fan
>            Assignee: Wenchen Fan
>            Priority: Major
>              Labels: release-notes
>             Fix For: 2.3.0
>
>
> un-aliased subquery is supported by Spark SQL for a long time. Its semantic was not well defined and has confusing behaviors, and it's not a standard SQL syntax, so we disallowed it in https://issues.apache.org/jira/browse/SPARK-20690 .
> However, this is a breaking change, and we do have existing queries using un-aliased subquery. We should add the support back and fix its semantic.
> After the fix, there is no syntax change from branch 2.2 to master, but we invalid a weird use case:
> {{SELECT v.i from (SELECT i FROM v)}}. Now this query will throw analysis exception because users should not be able to use the qualifier inside a subquery.



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