public Collection<Equipa> values(String cod_competicao){
         try {
            Collection<Equipa> col = new HashSet<Equipa>();
            Statement stm = conn.createStatement();
            ResultSet rs = stm.executeQuery("SELECT Equipa.* FROM Equipa,EquipaCampeonato where EquipaCampeonato.cod_equipa=Equipa.cod_equipa and EquipaCampeonato.cod_competicao='"+cod_competicao+"'");
            
            for (; rs.next();) {

                col.add(new Equipa(rs.getString(1), rs.getString(2),rs.getString(3),rs.getString(4)));
            }
            rs.close();
            stm.close();
            return col;
        } catch (SQLException | NumberFormatException e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
            return null;
        }
    }