SELECT T1.ROW1, T1.ROW2, T2.ROW1, T2.ROW2 FROM TABLE1 T1, TABLE2 T2

OracleConnection connec = new OracleConnection("user id=пользователь;password=пароль;data source=ссылка на БД (сид)");
string select = "SELECT T1.ROW1, T1.ROW2, T2.ROW1, T2.ROW2 FROM TABLE1 T1, TABLE2 T2"
try
            {
                connec.Open();
                OracleCommand cmd = new OracleCommand(select , connec);
                OracleDataReader rdr = cmd.ExecuteReader();

                
                GridView1.ShowHeader = true;
                GridView1.DataSource = rdr;
                GridView1.DataBind();
            }
            catch (OracleException ex)
            {
                label.text = "Ошибка: " + ex.Message;

            }
            finally
            {
                connec.Close();
            }