In your data model, the two tables are not associated, which is not ideal... Preferably, you'd like to associate your events with the participating stores, etc...
Within your structure, I'd suggest to use the ONLY() function for the store count. This technique, however, requires that one and only one event (or, technically speaking one single store count) is selected in order to enable the calculation. See attached file.
test.qvf 192.0 K
Thanks. it works. but I found another problem.
The store count in my sample was static, which is fine with your solution.
But in real world, the value is calculated value. I attached a further sample.
In this updated sample, I got error saying bad field name.
Can you help me out again? thanks again.
test-updated.qvf 192.0 K