public static void update(String ID, String name, String pwd, String comments){     //update䣬޸һ
        String sqlDelete;       //sql
        name="'"+name+"'";
        pwd="'"+pwd+"'";
        comments="'"+comments+"'";
        sql="INSERT INTO Pwd VALUES "+"("+ID+","+name+","+pwd+","+comments+")";

        sqlDelete="DELETE FROM pwd WHERE  ID= "+ID;     //ɾԭ
        DB.sql(sqlDelete);
        DB.sql(sql);            //޸ĺݣ޸Ч
    }