java.sql.SQLException:[SQLITE_ERROR] SQL 错误或缺少数据库（靠近“=”：语法错误）
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java.sql.SQLException:[SQLITE_ERROR] SQL error or missing database (near "=":syntax error)
提问by Mike Nguyen
I made the sqlite database using the firefox web development thing, saved it to my pc but I ran into some problem while linking the database. Whenever I click the login button to test I get "java.sql.SQLException:[SQLITE_ERROR] SQL error or missing database (near "=":syntax error)". He advise me to change the "//" to "\" within the database class and see if it worked but it didn't so if someone could look at the code and help me out it would greatly appreciated.
我使用 firefox Web 开发工具制作了 sqlite 数据库，并将其保存到我的电脑上，但是在链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，我都会收到“java.sql.SQLException:[SQLITE_ERROR] SQL 错误或缺少数据库（靠近“=”：语法错误）”。他建议我将数据库类中的“//”更改为“\”，看看它是否有效，但它没有，所以如果有人可以查看代码并帮助我解决，我将不胜感激。
code for loader
装载机代码
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) {
}
}
}
}
main statement
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");
}
}
database class
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;
}
}
}
回答by Patashu
"SELECT = FROM Users WHERE Username=? AND Password=?"
"SELECT = FROM Users WHERE Username=? AND Password=?"
The first = is a syntax error. It should be like this
第一个 = 是语法错误。应该是这样的
"SELECT 1 FROM Users WHERE Username=? AND Password=?"
"SELECT 1 FROM Users WHERE Username=? AND Password=?"
Since you don't care about what's in the rows, you just want to count how many rows they are, so you return a dummy number 1 per row returned.
由于您不关心行中有什么，您只想计算它们有多少行，因此您返回一个虚拟数字 1，每返回一行。
If you want all of the fields of the row then you'd do this:
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=?"
"SELECT * FROM Users WHERE Username=? AND Password=?"
But =is a syntax error, you can't have =there.
但是=是语法错误，你不能=有。
