มีวิธีเช็คค่า textBox ว่าตรงกับ database มั้ยคับ ช่วยทีคับ..... C#.net นะคับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.IO;

namespace LoginFormCS
{
    public partial class frmLogin : Form
    {
        public frmLogin()
        {
            InitializeComponent();
        }

        private void btnLogin_Click(object sender, EventArgs e)
        {
            SqlConnection objConn = new SqlConnection();
            SqlCommand objCmd = new SqlCommand();
            string strConnString = null;
            string strSQL = null;

            strConnString = "Server=localhost;UID=sa;PASSWORD=;Database=mydatabase;Max Pool Size=400;Connect Timeout=600;";
            objConn.ConnectionString = strConnString;
            objConn.Open();

            int intNumRows = 0;
            strSQL = "SELECT COUNT(*) FROM member WHERE Username = '" + this.txtUsername.Text + "' AND Password = '" + this.txtPassword.Text + "' ";
            objCmd = new SqlCommand(strSQL, objConn);
            intNumRows = Convert.ToInt32(objCmd.ExecuteScalar());

            if (intNumRows > 0)
            {
                frmMain frm = new frmMain();
                frm._strUser = this.txtUsername.Text;
                frm.LoadInfor();
                frm.Show();

                this.Hide();
            }
            else
            {
                MessageBox.Show("Username or Password Incorrect");
            }

            objConn.Close();
            objConn = null;
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            if (MessageBox.Show("Exit application?", "", MessageBoxButtons.YesNo) == DialogResult.Yes)
            {
                Application.Exit();
            }
        }


    }
}