SQL & PL/SQL

hi all,
i need to creeate a cursor wich content depends on another cursor. how can i do that?
here an example

colonna1 varchar2(20);
cursor num_formule is
select distinct cod_output from table; 
TYPE cur IS REF CURSOR;      

begin

for colonna1 in num_formule
    loop
        open cur for 
        select fields from table2 where field1=colonna1.field;
        for colonna in cur
            loop
                sql_stmt:=sql_stmt||colonna.field;
        end loop;
        
        DBMS_OUTPUT.put_line(sql_stmt);
        
    end loop;

how can i do that?
thx