mysql - 如何仅使用 Jdbc 从 MySQL 验证后检索特定用户的数据？

Question

这是一个代码片段......我只是想让它在用户成功登录验证后检索该用户的信息......(我只使用jdbc和 Mysql 服务器，我从控制台获取输入......并假设数据库表有您选择的 4 个条目。)

表名称: 结果

我的表属性是: 名称|卷|数学|物理|化学

package com.connect.register;

import java.sql.*;
import java.util.*;

import static com.connect.register.Dbconnection.*;

public class ShowResult {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    Class.forName("com.mysql.jdbc.Driver");

    System.out.println("Connecting to a selected database...");
    conn = DriverManager.getConnection(URL, USER, PAS);
    System.out.println("Connected database successfully...");

    String SQL = "Select * from studentconnect.result Where Roll=?";

    System.out.println("Creating statement...");
    stmt = conn.prepareStatement(SQL);

    Scanner scn = new Scanner(System.in);
    System.out.print("Enter roll no. to see result:");
    int roll = scn.nextInt();
    scn.close();
    stmt.setInt(1, roll);

    rs = stmt.executeQuery();

    if (rs.next()) {
        System.out.println("Login Successfull");
        return;
    } else {
        System.out.println("Please enter Correct roll no.");
    }
    **while (rs==roll) {
        // Retrieve by column name
        String Name = rs.getString("Name");
        int Roll = rs.getInt("Roll");
        int Math = rs.getInt("Math");
        int Physics = rs.getInt("Physics");
        int Chemistry = rs.getInt("Chemistry");
        // Display values
        System.out.println("Name: " + Name);
        System.out.println("Roll: " + Roll);
        System.out.println("Math " + Math);
        System.out.println("Physics: " + Physics);
        System.out.println("Chemistry: " + Chemistry);
    }
    rs.close();**

}

}

Answer 1

如前所述，rs 与 roll 完全不同。 rs 代表包含所有已发送到数据库的查询响应的 ResulSet。由于您已在声明中输入了卷号，并且我假设卷号是唯一的，因此您的代码可能如下所示:

rs = stmt.executeQuery();
if ( rs.next()) {
  System.out.println("Login successfull");
  System.out.println("Name: " + rs.getString("Name") + "\n"
                   + "Roll: " + rs.getInt("Roll") + "\n"
                   + "Math: " + rs.getInt("Math") + "\n"
                   + "Physics: + rs.getInt("Physics") + "\n"
                   + "Chemistry: " + rs.getInt("Chemistry"));
  rs.close();    
} else {
  System.out.println("Please enter Correct roll no.");
}