Not sure if I got there, but maybe the below can give ideas.
I think there may a few issues at hand.
1. I think it may be better to make the sales datasource the primary
and the promo the secondary. I think that was partially causing the null
you were seeing because the ATTR() was returning an asterisk.
2. You may need to pull some fields from both sources onto the detail shelf
to establish the relationship between the two. Will to see how that works
our for your real data.
3. Will need to check the table calculation settings when totaling the volume.
Please see workbook v10.3 attached in the Forum Thread.
279014between.twbx 42.8 KB
Would you mind sharing this via Public?
Based on your advice I got the calculation to show for specific dates, but could not yet get the totaling/aggregation to work.
Apololgies, I think I got the version wrong,
not sure if you were able to open it from the Forum Thread.
Here it is on Public: