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https://issues.apache.org/jira/browse/TRAFODION-2418?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hans Zeller reopened TRAFODION-2418:
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Sorry, jumped the gun here. This fix is not yet checked in.
> Allow group by push-down to a fact table
> ----------------------------------------
>
> Key: TRAFODION-2418
> URL: https://issues.apache.org/jira/browse/TRAFODION-2418
> Project: Apache Trafodion
> Issue Type: Improvement
> Components: sql-cmp
> Reporter: Hans Zeller
> Assignee: Hans Zeller
> Fix For: 2.1-incubating
>
>
> Trafodion has a rule that pushes a groupby down over a join when possible,
> but it will not push the groupby to the left child of a join - it relies on
> join commutativity. This might have been ok 20 years ago when this was coded
> (by me...), but it isn't good for some situations today. Example:
> {noformat}
> select d.y, count(f.a), sum(f.b)
> from big_fact f join small_dim d on f.x=d.y
> where d.a = 1
> group by d.y
> {noformat}
> The plan we would like is a hash join with the group by on big_fact as the
> left child. To do this, we need to remove the heuristic that prevents this
> form of push-down.
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