SqlConnection sqlcon = new SqlConnection("Data Source=ServerName\\SQLEXPRESS; Initial Catalog=DataBaseName; Integrated Security=True");

protected void Page_Load(object sender, EventArgs e)
{
     if(!IsPostback)
     {
        BindDropDown1();
        BindDropDown2();
     }
}

void BindDropDown1()
{
sqlcon.Open();
SqlCommand cmd = new SqlCommand("select columnname from tablename");
SqlDataReader dr = cmd.ExecuteReader();
    While(dr.read())
    {
        drowdownlist1.datasource=dr;
        dropdownlist1.dataTextField="columnname";
        dropdownlist1.dataValueField="columnnameId";
        dropdownlist1.DataBind();
        sqlcon.close();
    }
}

void BindDropDown2()
{
sqlcon.Open();
SqlCommand cmd = new SqlCommand("select columnname from tablename");
SqlDataReader dr = cmd.ExecuteReader();
    While(dr.read())
    {
        drowdownlist1.datasource=dr;
        dropdownlist1.dataTextField="columnname";
        dropdownlist1.dataValueField="columnnameId";
        dropdownlist1.DataBind();
        sqlcon.close();
    }
}