Get multiple users to access the same asp.net-based session

protected void btn_Click(object sender, EventArgs e)
{
con.Open();
String myquery = "select * from S_register";
SqlCommand cmd = new SqlCommand();
cmd.CommandText = myquery;
cmd.Connection = con;
SqlDataAdapter da = new SqlDataAdapter();
da.SelectCommand = cmd;
DataSet ds = new DataSet();
da.Fill(ds);
String uname;
String pass;
uname = ds.Tables[0].Rows[1]["id"].ToString();
pass = ds.Tables[0].Rows[1]["passcode"].ToString();
con.Close();
if (uname == TextBox1.Text && pass == TextBox2.Text)
{
Session["username"] = uname;
Response.Redirect("Login_successfull_user.aspx");
}
else
{
L1.Text = "Invalid Username or Password - Relogin with Correct Username Password";
}

The above code make only one credentiol to login which is present at the first row of register table.What is the solution fon make login with other user credentials