I have a table with a timestamp field. I need to do a count, and a sum on a
field each and group by the month.

I know I can use extract to get the month and group by that, but I am
assuming that in such a case FB will not be able to use an index and as the
number of records grows this will be very slow? Is the best option then to
make a number, month field and keep this field up to date and indexed?