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https://issues.apache.org/jira/browse/CALCITE-4015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17111375#comment-17111375
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Haisheng Yuan commented on CALCITE-4015:
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It is open for pick up.
> Pass through parent collation request on subset or superset of join keys for
> EnumerableMergeJoin
> ------------------------------------------------------------------------------------------------
>
> Key: CALCITE-4015
> URL: https://issues.apache.org/jira/browse/CALCITE-4015
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Haisheng Yuan
> Priority: Major
>
> Pass through parent collation request on subset or superset of join keys for
> EnumerableMergeJoin.
> e.g.
> {code:java}
> select * from foo join bar on foo.a=bar.a and foo.b=bar.b order by b;
> {code}
> collation on b is passed to mergejoin, mergejoin should generate an
> alternative with collation on b, a.
> {code:java}
> select * from foo join bar on foo.a=bar.a and foo.b=bar.b order by foo.a,
> foo.b, foo.c;
> {code}
> collation on a,b,c is passed to mergejoin, mergejoin should generate an
> alternative with collation on a,b,c, even the join keys are a,b, but since
> foo.c is also the output column, mergejoin can still request its child foo to
> deliver collation on a,b,c. The join keys must be the collation request's
> prefixes.
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