如何在JAVA中查询两个数据相似的表，并将结果按表字段分组？

import java.sql.*;

public class TableQuery {
    public static void main(String[] args) {
        // 数据库连接信息
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String username = "root";
        String password = "password";

        // SQL查询语句
        String sql = "SELECT t1.field1, t1.field2, t2.field3 " +
                     "FROM table1 t1, table2 t2 " +
                     "WHERE t1.field1 = t2.field1 " +
                     "GROUP BY t1.field1";

        try {
            // 连接数据库
            Connection connection = DriverManager.getConnection(url, username, password);

            // 执行查询
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);

            // 处理查询结果
            while (resultSet.next()) {
                String field1 = resultSet.getString("field1");
                String field2 = resultSet.getString("field2");
                String field3 = resultSet.getString("field3");

                // 按表字段进行分组处理
                // TODO: 进行分组处理的逻辑

                System.out.println("field1: " + field1 + ", field2: " + field2 + ", field3: " + field3);
            }

            // 关闭连接
            resultSet.close();
            statement.close();
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}