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From hvanhovell <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-11275][SQL][WIP] Rollup and Cube Genera...
Date Mon, 02 Nov 2015 20:26:17 GMT
Github user hvanhovell commented on the pull request:

    https://github.com/apache/spark/pull/9419#issuecomment-153146768
  
    If I understand the problem correctly, the logical Expand operator makes items which are
not in the grouping set ```null```. This means that if a column is both used for grouping
and for aggregation and that column is not in the grouping set, this column will be set to
```null``` and the aggregate will also become ```null``` (which is not correct).
    
    What I don't understand is why we are not fixing the logical Expand by introducing two
sets of expressions, one for grouping and one for aggregation. This is much simpler and fixes
the problem at its root.


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