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From zellerh <>
Subject [GitHub] incubator-trafodion pull request #893: [TRAFODION-2418] Allow group by push-...
Date Fri, 23 Dec 2016 19:31:22 GMT
GitHub user zellerh opened a pull request:

    [TRAFODION-2418] Allow group by push-down to a fact table

    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:
        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
    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.

You can merge this pull request into a Git repository by running:

    $ git pull bug/2418

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #893
commit 7894cc88b4ffe5ecdfdbf353453e0e0315d26b01
Author: Hans Zeller <>
Date:   2016-12-23T19:25:47Z

    [TRAFODION-2418] Allow group by push-down to a fact table


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