Here's the scenario:

Dataset1:

Select *

from MyTable

Where Period Between @StartPeriod AND @EndPeriod; --- Works like a charm

Dataset2:

Select *

from MyTable

Where Period = @Period;

@Period should get its values from @EndPeriod.

The idea is: Headcount report showing monthly staff headcount in a table and Year to Date growth in a graph. Dataset1 would populate the graph while dataset2 populates the table