java.sql.SQLException：[SQLITE_ERROR] SQL 错误或缺少数据库(接近"="：语法错误)

Question

我使用firefox web开发的东西做了sqlite数据库，保存到我的电脑，但我在连接数据库时遇到了一些问题。每当我单击登录按钮进行测试时，都会得到"java.sql。SQLException:[SQLITE_ERROR] SQL错误或缺少数据库(接近"=":语法错误)"。他建议我将数据库类中的"//"改为""，看看它是否有效，但它没有，所以如果有人能看看代码并帮助我，那将非常感激。

加载器代码

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class Loader extends JFrame implements ActionListener{
private static final long serialVersionUID = 1L;
JLabel username;
JTextField userField;
JButton register;
JLabel password;
JPasswordField passField;
JButton login;
ImageIcon logo;
JLabel imageLogo;
Connection conn = null;
ResultSet rs = null;
PreparedStatement ps = null;
Loader() {
conn = DBConnect.ConnectDB();
setLayout(null);
username = new JLabel("Username");
username.setBounds(100, 75, 75, 75);
userField = new JTextField("", 10);
userField.setBounds(162, 102, 90, 20);
register = new JButton("Register");
register.setForeground(Color.white);
register.setBackground(Color.black);
register.setBounds(275, 95, 90, 30);
password = new JLabel("Password");
password.setBounds(100, 105, 75, 75);
passField = new JPasswordField();
passField.setBounds(162, 132, 90, 20);
login = new JButton("Login");
login.addActionListener(this);
login.setBounds(275, 125, 90, 30);
login.setForeground(Color.white);
login.setBackground(Color.black);
logo = new ImageIcon(getClass().getResource("nameless.png"));
imageLogo = new JLabel(logo);
imageLogo.setBounds(110, 25, 250, 40);
add(username);
add(userField);
add(register);
add(password);
add(passField);
add(login);
add(imageLogo);
}
@Override
public void actionPerformed(ActionEvent e) {
String sql = "SELECT = FROM Users WHERE Username=? AND Password=?";
try{
ps = conn.prepareStatement(sql);
ps.setString(1, userField.getText());
ps.setString(2, passField.getText());
rs = ps.executeQuery();
if(rs.next()){
JOptionPane.showMessageDialog(null, "Logged In!", "Logged In", JOptionPane.INFORMATION_MESSAGE);
}else{
JOptionPane.showMessageDialog(null, "Invalid Detail.nPlease Try Agian.", "Error", JOptionPane.ERROR_MESSAGE);
userField.setText("");
passField.setText("");
}
}catch(Exception a){
JOptionPane.showMessageDialog(null, a);
}
finally {
try{
rs.close();
ps.close();
}catch(Exception a) {
}
}
}
}

主要声明

import javax.swing.JFrame;
public class MainStatement {
public static void main(String Args[]) {
Loader l = new Loader();
l.setVisible(true);
l.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
l.setResizable(false);
l.setSize(450, 200);
l.setTitle("Nameless™ Database");
}
}

数据库类

import java.sql.Connection;
import java.sql.DriverManager;
import javax.swing.JOptionPane;
public class DBConnect {
public static Connection ConnectDB(){
try{
Class.forName("org.sqlite.JDBC");
Connection conn = DriverManager.getConnection("jdbc:sqlite:C:\Users\YellowMilk\Folders\Private\Java\NamelessDatabase.sqli​te");
return conn;
}catch(Exception e){
JOptionPane.showMessageDialog(null, e);
return null;
}
}
}

Answer 1

"SELECT = FROM Users WHERE Username=? AND Password=?"

第一个=是语法错误。应该是这样的

"SELECT 1 FROM Users WHERE Username=? AND Password=?"

由于您不关心行中有什么，您只想计算它们有多少行，因此您每返回一行返回一个虚拟数字1。

如果您想要该行的所有字段，那么您可以这样做:

"SELECT * FROM Users WHERE Username=? AND Password=?"

但=是一个语法错误，你不能有=在那里