///////////////////
接下来我们重新在原来之前数据库中创建一个表
mysql> CREATE TABLE admin(
    -> id int auto_increment,
    -> loginpwd varchar(20) not null,
    -> loginid varchar(30) not null,
    -> PRIMARY KEY ( id )
    -> )ENGINE=InnoDB DEFAULT CHARSET=utf8;

在插入数据
insert admin(loginpwd,loginid) value('admin','admin'),('jack','123456');

最终结果
mysql> select * from admin;
+----+----------+---------+
| id | loginpwd | loginid |
+----+----------+---------+
|  1 | admin    | admin   |
|  2 | jack     | 123456  |
+----+----------+---------+

你的登录名叫admin，密码为admin，或者你的另一个登录名叫123456，密码为jack

接下来我们查询数据
select * from admin where loginid='admin' and loginpwd='admin';

/////////////////
接下来我们在运行下面这段java代码
它可以检查你输入的登录名和密码与库中的是否匹配

package abc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Scanner;

public class MySQL1 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
		System.out.print("用户名:");
		String loginid = input.next();
		System.out.print("密   码:");
		String loginpwd = input.next();
		
		String sql = "select * from admin where loginid='"+loginid+"' and loginpwd='"+loginpwd+"';";
		try {
			Class.forName("com.mysql.cj.jdbc.Driver");
			Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/RUNOOB?useSSL=false&serverTimezone=UTC","root", "");
			PreparedStatement ps = connection.prepareStatement(sql);
			ResultSet rs =  ps.executeQuery();
			if(rs.next()) {
				System.out.println("登录成功");
			}else {
				System.out.println("登录失败");
			}
			rs.close();
			ps.close();
			connection.close();
			}catch(Exception e) {
				e.printStackTrace();
			}
		}
}