problems selecting multiple records (again!)

hi everyone,
i already wrote to this list for the same problem.... i thought i had
resolved it, but i was wrong !
i'll explain my problem in a different (and simplier to understand) way:

suppose you have a table representing some events like this:

id | ref | date
-----------------------
1 | 10 | 2001-05-10
2 | 10 | 2001-05-11
3 | 10 | 2001-05-12
4 | 20 | 2001-05-11
5 | 20 | 2001-05-13
6 | 30 | 2001-05-15

the "ref" field is used to match this table with an another table containing
the description of the event in that date.
So, in this example I have the same event (identified as '10') which is
repeated 3 times, another event ('20') repeated twice, and an event with a
single occurance ('30').
now suppose that today is 2001-05-09 and i want to publish on my web-site
the next 3 events:

doing a simple SELECT i will get :

1 | 10 | 2001-05-10
2 | 10 | 2001-05-11
4 | 20 | 2001-05-11

but what i really wanted was :

1 | 10 | 2001-05-10
4 | 20 | 2001-05-11
6 | 30 | 2001-05-15

i.e., i don't want to get more than one occurance of the same "ref".

plz help me since i'm getting crazy trying to solve this problem !!!
keep in mind that i'll have a table with hundreds of event, so the faster
way to get the result is the preferred :-)

the web publishing system is based on zope.

tnx for your help

Giorgio A.