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https://issues.apache.org/jira/browse/SPARK-28166?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dongjoon Hyun updated SPARK-28166:
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Affects Version/s: (was: 3.0.0)
3.1.0
> Query optimization for symmetric difference / disjunctive union of Datasets
> ---------------------------------------------------------------------------
>
> Key: SPARK-28166
> URL: https://issues.apache.org/jira/browse/SPARK-28166
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 3.1.0
> Reporter: Josh Rosen
> Priority: Minor
>
> The *symmetric difference* (a.k.a. *disjunctive union*) of two sets is their
> set union minus their set intersection: it returns tuples which are in only
> one of the sets and omits tuples which are present in both sets (see
> [https://en.wikipedia.org/wiki/Symmetric_difference]).
> With the Datasets API, we can express this as either
> {code:java}
> a.union(b).except(a.intersect(b)){code}
> or
> {code:java}
> a.except(b).union(b.except(a)){code}
> Spark currently plan this query with two joins. However, it may be more
> efficient to represent this as a full outer join followed by a filter and a
> distinct (and, depending on the number of duplicates, we might want to push
> additional distinct clauses beneath the join, but I think that's a separate
> optimization). It would cool if the optimizer could automatically perform
> this rewrite.
> This is a very low priority: I'm filing this ticket mostly for tracking /
> reference purposes (so searches for 'symmetric difference' turn up something
> useful in Spark's JIRA).
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