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:<br><br>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.
<br><br>2) It will also bring greater consistency to how count distinct and summable measures are evaluated.<br><br><br><br><div class="gmail_quote">On Jan 22, 2008 7:52 PM, Julian Hyde <<a href="mailto:jhyde@pentaho.org">
jhyde@pentaho.org</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<div dir="ltr" align="left"><span><font color="#000080" face="Verdana" size="2">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.</font></span></div>
<div dir="ltr" align="left"><span><font color="#000080" face="Verdana" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#000080" face="Verdana" size="2">Would this work with distinct-count measures applied to
aggregate members? (For example unit sales over [CA plus
OR].)</font></span></div>
<div dir="ltr" align="left"><span><font color="#000080" face="Verdana" size="2"></font></span> </div>
<div dir="ltr" align="left"><span><font color="#000080" face="Verdana" size="2">Julian</font></span></div><br>
<blockquote style="border-left: 2px solid rgb(0, 0, 128); padding-left: 5px; margin-left: 5px; margin-right: 0px;">
<div dir="ltr" align="left" lang="en-us">
<hr>
<font face="Tahoma" size="2"><b>From:</b> <a href="mailto:mondrian-bounces@pentaho.org" target="_blank">mondrian-bounces@pentaho.org</a>
[mailto:<a href="mailto:mondrian-bounces@pentaho.org" target="_blank">mondrian-bounces@pentaho.org</a>] <b>On Behalf Of </b>Ajit Vasudeo
Joglekar<br><b>Sent:</b> Tuesday, January 22, 2008 9:33 AM<br><b>To:</b>
<a href="mailto:mondrian@pentaho.org" target="_blank">mondrian@pentaho.org</a><br><b>Subject:</b> [Mondrian] Adding Grouping Set support
for Distinct Count measures<br></font><br></div><div><div></div><div class="Wj3C7c">
<div></div><br><font face="sans-serif" size="2">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.</font> <br><br><font face="sans-serif" size="2">It will be
great if we can make this a part of the upcoming release. Requesting
comments</font> <br><br><font face="sans-serif" size="2">Thanks</font>
<br><br><font face="sans-serif" size="2">-Ajit</font>
<br><br></div></div></blockquote></div>
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