Select only active entries

Hi,

I have a table that looks as follow:

=# SELECT id, is_active FROM test_select;
  id | is_active
----+-----------
   5 | t
   5 | f
   6 | t
   7 | t
   8 | t
   5 | t
   8 | f
   9 | t
  10 | t
   6 | f
  10 | f
(11 rows)

I want to create a query to select only the latest ones that are
active, is there an easy way to do this or should I rethink my design?
The table will not be very big? (I am very new to PostgreSQL and
select queries)

I want the following result from a select query:
=#SELECT id, is_active FROM test_select WHERE <where conditions>;
  id | is_active
----+-----------
   5 | t
   7 | t
   9 | t
(3 rows)

I cant assume that those with uneven number of entries are active
since one can have the situation where one sets it active and then
sets it active again and then deactivates it. Or should I rather make
sure this does not happen and then return all the entries with an
uneven number of entries? How would such a query look to return the
uneven entries?

I cant use update since I want to retain the history of what happened when.

Any help will be appreciated.
Using: PostgreSQL 8.4 on Ubuntu 10.04


--
Carel Combrink
s25291930@tuks.co.za

This message and attachments are subject to a disclaimer. Please refer
to www.it.up.ac.za/documentation/governance/disclaimer/ for full
details. / Hierdie boodskap en aanhangsels is aan 'n vrywaringsklousule
onderhewig. Volledige besonderhede is by
www.it.up.ac.za/documentation/governance/disclaimer/ beskikbaar.