做动态asp网页的时候在应用程序中加数据源跟写代码的数据源有什么区别~

目前没发现区别.
public partial class index : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}
protected void Button1_Click(object sender, EventArgs e)
{
String con = "server=.;database=mdb;uid=sa;pwd=";
SqlConnection conn = new SqlConnection(con);

conn.Open();
String sql = "select username,[password],fullname,degree from username where username='" + TextBox1.Text + "'";

SqlCommand cmd=new SqlCommand(sql,conn);
SqlDataReader reader=cmd.ExecuteReader();
if(reader.Read())
{
if((string)reader["password"]!=TextBox2.Text)
{
Response.Write("密码有误!");
return;
}
}
else
{
Label4.Text="无效用户名!";
return;
}
Session["username"]=reader["username"].ToString();
Session["fullname"]=reader["fullnam