public List<To_DingDan> findByHyId3(Integer id) throws Exception{
        String sql = "select * from (select * from to_dingdan t where t.hyid="+id+" and t.type='待付款' order by t.id desc) j group by j.hyid2 order by j.id desc";
        // 获取到连接
        List<To_DingDan> list = new ArrayList<To_DingDan>();
        // 获取到连接
        //加载驱动
        Class.forName("com.mysql.jdbc.Driver");
        //获取连接Connection
        Connection conn = (Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/jiaju4?useUnicode=true&characterEncoding=UTF8", "root", "123456");
        //得到执行sql语句的对象Statement
        Statement stmt = (Statement) conn.createStatement();
        //执行sql语句，并返回结果
        ResultSet rs = (ResultSet) stmt.executeQuery(sql);
        
        //rs.next()在本地为true 部署到服务器为false
        while (rs.next()) {
            // 将查询出的内容添加到list中，其中userName为数据库中的字段名称
            System.out.println("++++++++++++++++++++++++++++++++++++++++++++++++++++++");
            To_DingDan dd = new To_DingDan();
            dd.setHyid2(rs.getInt("hyid2"));
            list.add(dd);
        }
        rs.close();
        stmt.close();
        conn.close();
        System.out.println(list.size()+"******************");
        return list;
    }

首先数据库字段，格式，用户名，密码完全一样。