I am receiving inconsistent results from almost the same query that i
am running.

Below is the query.

==================
part 1:

select distinct su.card_id, su.usage_date
from scratch_card_usage su
join scratch_cards sc on su.card_id = sc.id
where sc.card_type_id in (9, 10)
and (su.usage_date <= '30-dec-2005' and su.usage_date >= '1-dec-2005')

union

select distinct su.card_id, su.usage_date
from scratch_card_usage su
join scratch_cards sc on su.card_id = sc.id
where sc.card_type_id in (9, 10)
and (su.usage_date <= '30-nov-2005' and su.usage_date >= '1-nov-2005')

========================


========================
part 2:

select distinct su.card_id, su.usage_date
from scratch_card_usage su
join scratch_cards sc on su.card_id = sc.id
where sc.card_type_id in (9, 10)
and (su.usage_date between '1-nov-2005' and '30-dec-2005')


========================
Problem:
The records returned by both queries are not the same. I have gone
thru it like a 100 times cant find out where am going wrong. Is the
query wrong or is there a problem with Firebird? I have attached a
backup of the database as, "odd_behavious.fbk". Please i would
appreciate any response.


Specs:
1. Firebird 1.5.4172
2. Windows XP
3. IB Expert