Hans Zeller created TRAFODION-2418:
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Summary: 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
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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