Obscure MDX Month: Deselecting Members In An Excel PivotTable Leads To Missing Rows

Here’s some interesting (and borderline buggy) Excel PivotTable behaviour I learned about today from Charles-Henri Sauget, as well as the workaround for it courtesy of the great Greg Galloway.

Say you have a large dimension attribute hierarchy with 200,000 members on it in SSAS MD (or the equivalent in Tabular or Power Pivot) and drop it onto the rows of an Excel PivotTable. As you would expect, you get a PivotTable with 200,000 rows in it:

However if you then deselect just one member on rows like so:

…you’ll find that the PivotTable does not have 199,999 rows – in Excel 2016 it only has 32,000 rows:

(different versions of Excel may return different numbers of rows here, but still not the full number).

If you look at the MDX generated by Excel it consists of all of the member unique names that are still selected, and unsurprisingly it’s a gigantic query:

However, it turns out you can make Excel do the sensible thing and use the Except() function to return everything apart from the deselected member by going to the Field Settings dialog and selecting “Include new items in manual filter”:

This then gives you the expected number of rows in the PivotTable:

I suspect the reason Excel is generating the crazy-long MDX statement by default is that it’s the only way to prevent new members being added to the PivotTable if they are added to the attribute hierarchy in future. On a really large attribute hierarchy, though, the risk is that the resulting MDX query might exceed the maximum length of a query, so Excel has to truncate the number of members returned to make the query shorter. With “Include new items in manual filter” selected, though, it’s ok if new members do get added to the PivotTable in the future so it’s ok to use the Except() function in the query.