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Posted to issues@trafodion.apache.org by "ASF GitHub Bot (JIRA)" <ji...@apache.org> on 2017/01/03 17:23:58 UTC
[jira] [Commented] (TRAFODION-2418) Allow group by push-down to a
fact table
[ https://issues.apache.org/jira/browse/TRAFODION-2418?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15795586#comment-15795586 ]
ASF GitHub Bot commented on TRAFODION-2418:
-------------------------------------------
Github user asfgit closed the pull request at:
https://github.com/apache/incubator-trafodion/pull/893
> 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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