create or replace procedure phone_links (res out clob) as
  formonth date default trunc(add_months(sysdate, -1), 'month');
  login    varchar2(128);
  code     varchar2(3);


begin
  for c in (select conclusion
              from invoice
             where 1 = 1
               and invoice_date = formonth
               and thread_id >= 3
             group by conclusion) loop
    res := res ||
           'https://...?login=' ||
           login || '&ticket=' || href_hash || chr(13) || chr(10);
  end loop;
end;

using (OracleConnection oca = new OracleConnection("..."))
            {
                oca.Open();
                using (OracleCommand ocmd = new OracleCommand())
                {
                    ocmd.Connection = oca;
                    ocmd.CommandType = System.Data.CommandType.StoredProcedure;
                    ocmd.CommandText = "phone_links";
                    ocmd.InitialLOBFetchSize = 8192;

                    OracleParameter op = new OracleParameter();
                    op.ParameterName = "res";
                    op.Direction = ParameterDirection.Output;
                    op.OracleDbType = OracleDbType.Clob;

                    ocmd.Parameters.Add(op);


                    OracleDataReader odr = ocmd.ExecuteReader();

                    if (odr.HasRows)
                        rtbLinks.Text = odr.GetOracleClob(0).Value;
                    else
                        rtbLinks.Text = "No rows. ";
                }
                oca.Close();
            }