I wonder if someone can help me please?

I am looking to develop a dashboard in APEX to display approvals hierarchy for  requisitions and POs. Any of the SQL's I have tried so far only displays current approver. I am looking a way to generate whole list of approvers including the delagation etc. I tried using Approval_history table which does not update if the approval is delegated. any suggestions please?

current SQL:

SELECT distinct reqh.segment1 req,

         --reqh.wf_item_key,

         reqh.attribute10 Purchase_category,

         cre_usr.user_name creator,

         c_wit.item_type,

         reqh.description req_description,

         c_wias.assigned_user,

         c_wias.activity_result_code,