asp.net自己写代码实现用户和密码登陆时，怎么关联在SQL数据库中的用户和密码？

把你的用户名和密码输入以后，查询数据库里的用户表！
下面是一个普通的登录验证的代码！

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class Login : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void Button1_Click(object sender, EventArgs e)
{
string uid=txtCardId.Text;
string pwd=TxtPwd.Text;
bool flag = false;
SqlConnection con = new SqlConnection("server=.;database=bank;uid=sa;pwd=sa");
SqlDataAdapter adp = new SqlDataAdapter("select * from bankcard",con);
DataSet ds = new DataSet();
adp.