java mysql返回值为空

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class MySQLExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "username";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT * FROM mytable WHERE id = 1")) {

            if (rs.next()) {
                System.out.println("Result found: " + rs.getString("columnName"));
            } else {
                System.out.println("No result found.");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}