Fixed value dff segment with sql table value set

Hello experts,

We have the following requirement:

Create a segment in positions dff that needs to display the vacant fte as a delta between position fte and the sum of FTE value of each of the position incumbents.

To achieve this we have created a position_id dff where we store the position id from hr all positions on which to base our value set/sql.

The issue that we are facing is that the values are being displayed in the segment as a drop down list for the user to choose and we would like it to be as calculated value, that updates itself when the position is being displayed without user input.