C#

public class CustomerClass
    {
      SqlConnection con = new SqlConnection("server=(local);database=Tailor;integrated security=true;");
      SqlDataAdapter da = new SqlDataAdapter();
      DataSet ds = new DataSet();
      public CustomerClass()
        {
            
        }
        public  object selectCustomers()
        {
            con.Open();
            
            SqlCommand select = new SqlCommand("select * from Customers",con);
            select.ExecuteNonQuery();
            con.Close();
            da.SelectCommand = select;
            da.Fill(ds, "Customer");
            return ds.Tables;
        }
    }

CustomerClass test=new CustomerClass();
            object test2 = test.selectCustomers();
            dataGridView1.DataSource = test2;

string strSQLconnection = "Data Source=dbServer;Initial Catalog=testDB;Integrated Security=True";
SqlConnection sqlConnection = new SqlConnection(strSQLconnection);
SqlCommand sqlCommand = new SqlCommand("select * from mytable", sqlConnection);

sqlConnection.Open();
SqlDataReader reader = sqlCommand.ExecuteReader();

GridView1.DataSource = reader;
GridView1.DataBind();