Question

我正在尝试编写一个类，它将接受来自一个quizgame的两个字符串和一个int（用户名和密码以及分数），最终将来自GUI，我刚刚从它传递它们main，并将它们传递到要插入的数据库中。

我添加了JConnector jar文件并在Eclipse中工作。

这是我的代码

import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

//public 
class DbConnect {

    private java.sql.Connection con;
    private java.sql.Statement st;
    private ResultSet rs;

    public DbConnect() {
        try {
            Class.forName("com.mysql.jdbc.Driver");

            con = DriverManager.getConnection(
                    "jdbc:mysql://localhost:3307/nostalgic", "root", "usbw");

            st = con.createStatement();
        } catch (Exception ex) {
            System.out.println("Error is " + ex);
        }

    }

    public void setData(String n, String p, int x) {
        try {

            String query = "select * from nostalgic";
            String query1 = "INSERT INTO nostalgic values (n,p,x)";

            PreparedStatement statement3 = con.prepareStatement(query1);
            statement3.executeUpdate();

            rs = st.executeQuery(query);
            System.out.println("records from database");

            while (rs.next()) {
                String name1 = rs.getString("name");
                String pw = rs.getString("password");
                int score = rs.getInt("score");
                System.out.println("Name : " + name1);
                System.out.println("Password : " + pw);
                System.out.println("Score : " + score);
            }
        } catch (Exception ex) {
            System.out.println(ex);

        }

    }
}

我得到的错误是

'字段列表'中的未知列'n'

我可以像'john'那样直接输入一个字符串，但在这种情况下对我来说没用。

Answer 1

而不是INSERT INTO nostalgic values (n,p,x)你应该拥有 INSERT INTO nostalgic values (?,?,?)然后：

PreparedStatement statement3 = con.prepareStatement(query1);
statement3.setString(1,n);
statement3.setString(2,p);
statement3.setString(3,x);
statement3.executeUpdate();

Answer 2

in

String query1 = "INSERT INTO nostalgic values (n,p,x)";

n，p，x没有被这些值替换，它们只被视为一些char，这就是你得到这个错误的原因

编辑：statement3.executeUpdate();之前

        String query1 = "INSERT INTO nostalgic values (?,?,?)";

        PreparedStatement statement3 = con.prepareStatement(query1);
        statement3.setString(1,n);
        statement3.setString(2,p);
        statement3.setInt(3,x);

更新：您可能想知道为什么Unknown column 'n' in 'field list'？因为sql中的insert查询可以有这个结构

  INSERT INTO table (col1,col2,...) values (`val1`,`val2`,....)

但是如果硬编码，则值必须在``内;如果没有``符号则将其视为列名称。

Answer 3

米克问题是，在执行statement3.executeUpdate();时，您不会将实际参数传递给查询。请查看此链接以了解如何操作：http://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html。

Answer 4

你不能这样做试试这个：

            Class.forName("com.mysql.jdbc.Driver");
            try (Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3307/nostalgic","root","usbw") {
                PreparedStatement pr = null;
                String query = "INSERT INTO nostalgic VALUES ((?), (?), (?))";
                pr = con.prepareStatement(query);
                pr.setString(1, n);
                pr.setString(2, p);
                pr.setString(3, x);
                int status = pr.executeUpdate();
           }catch (ClassNotFoundException | SQLException e) {
            System.out.println(e.getMessage());
           }

Answer 5

您的代码中存在一些错误......

正确导入
插入声明

您的代码将是这样的：

import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Connection;
import java.jdbc.Statement;
// you imported sql innecessary statements...    


//public 
class DbConnect {

    // dont need complete path, you already imported it  
    private Connection con;
    private Statement st;
    private ResultSet rs;

    public DbConnect() {
        try {
            Class.forName("com.mysql.jdbc.Driver");

            con = DriverManager.getConnection(
                    "jdbc:mysql://localhost:3307/nostalgic", "root", "usbw");

            st = con.createStatement();
        } catch (Exception ex) {
            System.out.println("Error is " + ex);
        }

    }

    public void setData(String n, String p, int x) {
        try {

            String query = "select * from nostalgic";

            String query1 = "INSERT INTO nostalgic values (?,?,?)";
            // no need to define vars here, 
            // just number of places to be inserted here ----^ 

            PreparedStatement statement = con.prepareStatement(query1);
            // prepare statement
            statement = con.prepareStatement(query);
            // insert the variables in places you prepared before
            // and matching the types you need!!!
            statement.setString(1,n);
            statement.setString(2,p);
            statement.setInt(3,x);    
            rs = st.executeQuery(query);
            System.out.println("records from database");

            while (rs.next()) {
                String name1 = rs.getString("name");
                String pw = rs.getString("password");
                int score = rs.getInt("score");
                System.out.println("Name : " + name1);
                System.out.println("Password : " + pw);
                System.out.println("Score : " + score);
            }
        } catch (Exception ex) {
            System.out.println(ex);

        }

    }
}

class将java程序连接到数据库（接受参数）

5 个答案: