Solved: error in my pre-query

hi am having this error in my pre-query trigger ORA-00918: column ambiguously defined
SELECT CODE,DESCRIPTION,DESCRIPTION2 FROM (select ASS_APPL_CODE CODE,ASS_APPL_CODE CODE,ASS_APPL_DESC DESCRIPTION,ASS_APPL_DESC DESCRIPTION,null DESCRIPTION2 from IM_L_ASSOC_APPL_CODE order by 1)

the trigger code is

declare
	cursor c  is 
	    select column_name, column_id from all_tab_columns where table_name=:control.reftable and column_id<=3 order by column_id;
  r c%rowtype;	    
	
	q varchar2(2000) := '(select ';
	
	type arr is varray(3) of varchar2(50);
  arrv arr := arr('CODE', 'DESCRIPTION', 'DESCRIPTION2');
begin
	:control.column1:=null;
	:control.column2:=null;
	:control.column3:=null;

  open c ;
  loop
  	 fetch c into r;
  exit when c%notfound;	 
      q := q  || r.column_name||' '|| arrv(r.column_id)||',';
      if r.column_id = 1 then
      	:control.column1:=r.column_name;
      end if;
      
      if r.column_id = 2 then
      	:control.column2:=r.column_name;
      end if;
      
      if r.column_id = 3 then
      	:control.column3:=r.column_name;
      end if;
  end loop;

  if r.column_id=2 then
  	q := q  || 'null' ||' '|| arrv(3)||',';
  end if;
  
  q := substr(q,1,length(q)-1) || ' from '||:control.reftable||' order by 1)';

  set_block_property ('LIST',query_data_source_name,q);
  
  if 	:control.column3 is null then
  	  set_item_property ('LIST.DESCRIPTION2',VISIBLE,property_false);
  	  set_item_property ('LIST.DESCRIPTION',width,385);
  else
  	  set_item_property ('LIST.DESCRIPTION2',visible,property_true);
  	  set_item_property ('LIST.DESCRIPTION2',enabled,property_true);
  	  set_item_property ('LIST.DESCRIPTION2',insert_allowed,property_true);
  	  set_item_property ('LIST.DESCRIPTION2',update_allowed,property_true);
  	  set_item_property ('LIST.DESCRIPTION2',navigable,property_true);
  	 
  	  set_item_property ('LIST.DESCRIPTION',width,192);
  end if;	
  close c;
end;

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am in 11g
i think the error is beacause the table column has change its no longer code description am in 11g