public Collection<String> getClassificacao(String cod_competicao){
         try {
            Collection<String> col = new ArrayList<String>();
            Statement stm = conn.createStatement();
            ResultSet rs = stm.executeQuery("select Equipa.Cod_equipa,Pontos,Golos from Equipa,Classificacao where cod_competicao='"+cod_competicao+"'and Classificacao.cod_equipa=equipa.cod_equipa order by Pontos desc, Golos desc ");
            
            for (; rs.next();) {
                
                col.add((rs.getString(1)+"_"+rs.getString(2)+"_"+rs.getString(3)));
            }
            return col;
        } catch (SQLException | NumberFormatException e) {
            JOptionPane.showMessageDialog(null, e.getMessage(), "ERROR", JOptionPane.ERROR_MESSAGE);
            return null;
        }
    }