"JOIN"-ing information from multiple categories ???

From semantic-mediawiki.org

Property chains with the syntax Has location.Has coordinates work in conditions, but unfortunately not in columns (and why?).

You can use template format instead, with a template containing a {{#show:}} call. Yes, the performance will be terrible.

06:29, 8 October 2012

If the result doesn't have too many events the performance can be perfectly acceptable. I do such things with the template format all the time and I have no complaints about performance. So the performance can be terrible yes, but can also fine.

17:05, 18 October 2012