Populating Display Item Value On Query In Oracle Forms

Write Post-Query trigger for the block you want to fetch the field value for display item.

Example

Begin
   Select Ename into :datablock.dspname
      from emp
      where ecode = :datablock.ecode;
   -- Field dspname in datablock will be populated with the value 
exception
   when others then
   -- you can ignore error  
      null; 
End;

You can write multiple plsql blocks in post-query trigger for different tables.