The formular works fine as long as i don't filter to specific dates for other diagrams. As soon as i filter the dates, i just got the volume of the 30 days within the selected days. I would like to get always back the full 30 days. But other selections (on other fields of the table) shall apply to the result.
I have cleared all date fields, with the exception of th Date_Daily (which is set in the expression itself). Whatever I choose, the correct value is responded.
Question now: I clear my Date_Monthly and my Date_Weekly field. Logical is that this will be excluded in the expression. But if I filter on some values out of my Date_Daily the correct data still is displayed (which is good). Is it because the filter set in the expression is overwriting the selection in the fields, if it is the same field?
Yes, I think this is correct: set modifier in a set expression override selections in these field.
You can keep your selections even when using set modifier by using set operators (i.e. intersection operator * or union operator +, depending on your needs, check the Help for more detail).
Question now: I clear my Date_Monthly and my Date_Weekly field. Logical is that this will be excluded in the expression.
I'm not sure if I understand. Date_Monthly and Date_Weekly will not be excluded, the set expression will just ignore any selections you've done in these fields, so only Date_Daily is determining the set of records to aggregate over.