COMBO BOX BIND WITH SQL IN ASP.NET

private void bindcombo()

    {

        string sql = "select * from qualification_m";

        DataSet ds = new DataSet();

        SqlDataAdapter da = new SqlDataAdapter();

        using (SqlConnection myConnection = new SqlConnection(connectionString))

        {

            myConnection.Open();

            SqlCommand myCommand = new SqlCommand(sql, myConnection);

            myCommand.ExecuteNonQuery();

            da.SelectCommand = myCommand;

            da.Fill(ds);

            ddlqualification.DataSource = ds;

            ddlqualification.DataBind();

            myConnection.Close();

        }

    }