How to populate DFF initial value dynamically

Summary

Hi, I want to create a DFF on Fix Asset --> Asste Addition Page.

Content

Hi, I want to create a DFF on Fix Asset --> Asset Addition Page.

I want to use sql to populate the inital value for the field. For this I want to pass two parameters to the sql query that are selected in the form

The Sql query would be like this 

select fcb.segment1 || '-' || fcb.segment2 || '-' || count(1) from fa_additions_b fa, fa_categories_b fcb
where fa.asset_category_id = fcb.category_id
and fcb.segment1 =:p_seg1
and fcb.segment2 =:p_seg2