[Mondrian] Adding Grouping Set support for Distinct Count measures

Matt Campbell mkambol at gmail.com
Thu Jan 24 10:37:53 EST 2008

We're interested in this change not so much for performance (although we
have seen some cases where it seems to improve performance) but because:

1) It will allow correct totaling in cases where a dimension table does not
join to every fact table row.  We can get over-counting in these cases
because the total query is fired separately without joining to the dimension
table.  I know in general dimension rows should be all-inclusive, ie have a
member value for each fact table row.  We have some good reasons for
violating this rule, though.

2) It will also bring greater consistency to how count distinct and summable
measures are evaluated.

On Jan 22, 2008 7:52 PM, Julian Hyde <jhyde at pentaho.org> wrote:

>  No objections in principle. Have you hand-generated such queries to see
> whether they are any improvement? It is possible that the queries do not
> yield any performance improvement, because distinct-count is difficult for a
> database to evaluate and therefore it might be difficult for the DBMS to
> find commonality between the different grouping sets.
> Would this work with distinct-count measures applied to aggregate members?
> (For example unit sales over [CA plus OR].)
> Julian
>  ------------------------------
> *From:* mondrian-bounces at pentaho.org [mailto:mondrian-bounces at pentaho.org]
> *On Behalf Of *Ajit Vasudeo Joglekar
> *Sent:* Tuesday, January 22, 2008 9:33 AM
> *To:* mondrian at pentaho.org
> *Subject:* [Mondrian] Adding Grouping Set support for Distinct Count
> measures
> We would like to introduce grouping sets support for distinct count
> measures in mondrian. We have analyzed this and it is a small change. Most
> of the work is around changing and adding test cases.
> It will be great if we can make this a part of the upcoming release.
> Requesting comments
> Thanks
> -Ajit
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> Mondrian at pentaho.org
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