using(ZipFile zip = new ZipFile())
{
   zip.Encryption = EncryptionAlgorithm.WinZipAes256;
   zip.Password = "MyPassword";
   zip.AddEntry("data1.txt", stream1);
   zip.AddEntry("data2.txt", stream2);
}

SqlCommand Cmd = new SqlCommand("select [Field1],[Field2] from [Table]", Conn);
SqlDataReader reader = Cmd.ExecuteReader();
MemoryStream ms = new MemoryStream();
SqlDataReaderToStream(reader, ref ms);
reader.Close();

static void SqlDataReaderToStream(SqlDataReader _reader, ref MemoryStream _ms)
{
   byte[] buffer = new byte[1024 * 1024]; // 1Мб
   int cnt = 0;
   string Delimiter = "\t";
   string Terminator = "\n";
   Encoding enc = Encoding.Unicode;
   _ms.Seek(0, SeekOrigin.Begin);
   // Unicode BOM FFFE
   _ms.Write(new byte[] { 0xFF, 0xFE }, 0, 2);
   //Пишем данные
   string Field = "";
   while (_reader.Read())
   {
      for (int i = 0; i < _reader.FieldCount; i++)
      {
         switch (_reader[i].GetType().ToString())
         {
            case "System.DateTime":
               Field = ((DateTime)_reader[i]).ToString("yyyy-MM-dd HH:mm:ss");
               break;
            case "System.Decimal":
               Field = _reader[i].ToString().Replace(",", ".");
               break;
            case "System.Double":
               Field = _reader[i].ToString().Replace(",", ".");
               break;
            default:
               Field = _reader[i].ToString().Replace(Delimiter, " ").Replace("\r", " ").Replace("\n", " ").Replace("  ", " ");
               if (Field.Length > 5000)
                  Field = Field.Substring(1, 5000);
               break;
         }
         if (i != _reader.FieldCount - 1)
            Field += Delimiter;
         else
            Field += Terminator;
         cnt = enc.GetBytes(Field, 0, Field.Length, buffer, 0);
         _ms.Write(buffer, 0, cnt);
      }
   }
   _ms.Position = 0;
}

using (ZipFile zip = new ZipFile())
{
   Stream stream = new MemoryStream();

   zip.AddEntry("text.txt", stream);
   stream.Write(new byte[] { 0xFF, 0xFE }, 0, 2);
   byte[] buffer = new byte[15000];
   
   using (SqlConnection Conn = new SqlConnection("Server=alpha;Database=ReferInfo;Integrated Security=false;User ID=sa;Pwd=Oj7s0Kde"))
   {
      Conn.Open();
      using (SqlCommand Cmd = new SqlCommand("select * from T_DEF order by [id]", Conn))
      {
         
         SqlDataReader reader = Cmd.ExecuteReader();
         string Delimiter = "\t";
         string Terminator = "\n";
         Encoding enc = Encoding.Unicode;
         while (reader.Read())
         {
            string Field = "";
            for (int i = 0; i < reader.FieldCount; i++)
            {
               switch (reader[i].GetType().ToString())
               {
                  case "System.DateTime":
                     Field = ((DateTime)reader[i]).ToString("yyyy-MM-dd HH:mm:ss");
                     break;
                  case "System.Decimal":
                     Field = reader[i].ToString().Replace(",", ".");
                     break;
                  case "System.Double":
                     Field = reader[i].ToString().Replace(",", ".");
                     break;
                  default:
                     Field = reader[i].ToString().Replace(Delimiter, " ").Replace("\r", " ").Replace("\n", " ").Replace("  ", " ");
                     if (Field.Length > 5000)
                        Field = Field.Substring(1, 5000);
                     break;
               }
               if (i != reader.FieldCount - 1)
                  Field += Delimiter;
               else
                  Field += Terminator;
               int cnt = enc.GetBytes(Field, 0, Field.Length, buffer, 0);
               stream.Write(buffer, 0, cnt);
            }
         }
         reader.Close();
      }
   }
   zip.Save(@"c:\test.zip");
}

public class ThroughMemoryStream : MemoryStream
{
    private long _position;

    public override bool CanSeek { get { return false; } }

    public override void Write(byte[] buffer, int offset, int count)
    {
        base.Write(buffer, offset, count);
        _position += count;
    }

    public override int Read(byte[] buffer, int offset, int count)
    {
        var msBuffer = GetBuffer();
        var realCount = Math.Min(Length, count);
        Array.Copy(msBuffer, 0, buffer, 0, realCount);

        Array.Copy(msBuffer, realCount, msBuffer, 0, Length - realCount);
        SetLength(Length - realCount);

        return (int)realCount;
    }

    public override long Position
    {
        get { return _position; } 
        set { throw new NotImplementedException(); }
    }
}