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Posted to issues@spark.apache.org by "Josh Rosen (JIRA)" <ji...@apache.org> on 2019/05/21 00:41:00 UTC
[jira] [Updated] (SPARK-27785) Introduce .joinWith() overloads for
typed inner joins of 3 or more tables
[ https://issues.apache.org/jira/browse/SPARK-27785?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Josh Rosen updated SPARK-27785:
-------------------------------
Summary: Introduce .joinWith() overloads for typed inner joins of 3 or more tables (was: Introduce .joinWith() overload for inner join of 3 or more tables)
> Introduce .joinWith() overloads for typed inner joins of 3 or more tables
> -------------------------------------------------------------------------
>
> Key: SPARK-27785
> URL: https://issues.apache.org/jira/browse/SPARK-27785
> Project: Spark
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 3.0.0
> Reporter: Josh Rosen
> Priority: Major
>
> Today it's rather painful to do a typed dataset join of more than two tables: {{Dataset[A].joinWith(Dataset[B])}} returns {{Dataset[(A, B)]}} so chaining on a third inner join requires users to specify a complicated join condition (referencing {{_1}}), resulting a doubly-nested schema like {{Dataset[((A, B), C)]}}. Things become even more painful if you want to layer on a fourth join. Using {{.map()}} to flatten the data into {{Dataset[(A, B, C)]}} has a performance penalty, too.
> To simplify this use case, I propose to introduce a new set of overloads of {{.joinWith}}, supporting joins of {{N > 2}} tables for {{N}} up to some reasonable number (say, 6). For example:
> {code:java}
> Dataset[T].joinWith[T1, T2](
> ds1: Dataset[T1],
> ds2: Dataset[T2]
> ): Dataset[(T, T1, T2)]
> Dataset[T].joinWith[T1, T2](
> ds1: Dataset[T1],
> ds2: Dataset[T2],
> ds3: Dataset[T3]
> ): Dataset[(T, T1, T2, T3)]{code}
> I propose to do this only for inner joins (consistent with the default join type for {{joinWith}} in case joins are not specified).
> I haven't though about this too much yet and am not committed to the API proposed above (it's just my initial idea), so I'm open to suggestions for alternative typed APIs for this.
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