private void button1_Click(object sender, EventArgs e)

    {
        string MyConnectionString = "server=localhost;user=root;database=yangbo;port=3306;password=yangbo6510;";
        MySqlConnection connection = new MySqlConnection(MyConnectionString);
        if (textBox_username.Text.Trim() == "" && textBox_password.Text.Trim() == "")
        {
            MessageBox.Show("请输入用户名和密码进行注册");
        }
        else
        {
            connection.Open();//连接到数据库
            string sql = "select * from usernp where username='" + textBox_username.Text.Trim() + "' ;";
            MySqlCommand cmd = new MySqlCommand(sql, connection);
            cmd.CommandType = CommandType.Text;
            MySqlDataReader sdr;
            sdr = cmd.ExecuteReader();
            if (sdr.Read())
            {
                MessageBox.Show("用户名重复，请重新输入");
                textBox_username.Clear();
                textBox_password.Clear();
            }
            else
            {
                string sql1 = "insert into usernp (username,userpassword) values(' + textBox_username.Text.Trim() + ',' + textBox_password.Text.Trim() +')";
                cmd = new MySqlCommand(sql1, connection);
                int i = cmd.ExecuteNonQuery();
                if (i> 0)
                {
                    MessageBox.Show("注册成功");
                    textBox_username.Clear();
                    textBox_password.Clear();
                }
                
                else{
                    MessageBox.Show("注册不成功");
                    textBox_username.Clear();
                    textBox_password.Clear();
                }
            }
            connection.Close();
        }
    }