Inner Join Multiplies Results....

Hi, i guess u have run into it again..
I have 3 tables
Table 1 is holding word documents :
WordDoc
wd_id integer primary key
wd image

Table 2 is holding parts of the document in a master detail fashion as from one document we can create many parts of it.

WordPartDoc
wpd_id integer primary key
wpd_wd_id integer foreign key from WordDoc
wpd_part image


Table 3 holds the persons or groups to whom we have given a copy of a specific part.

PersonsCopiedAt
pca_id integer primarey key
pca_wpd_id integer foreing key from WordPartDoc
pca_pg_id integer this is the id of the table that holds the persons or the id of the table that holds the group
pca_p_or_g char(1) this is a flag : 'P' for a person, 'G' for a group

Now, here is my problem... I have created the following sql query
select wd_id, wpd_id
from wordDoc
inner join wordPartDoc on wpd_wd_id = wd_id
inner join PersonCopiedAt on pca_wpd_id = wpd_id
where pca_pg_id = someID and pca_p_or_g = 'G' --or 'P'

This works perfectly if a pca_pg_id is provided, but this is provided using a combobox... If the user doesn't select a person - and thus - no id is provided - inner join brings me as many records of wpd_id as the number of persons that were given a copy. I understand that this is the correct behaviour but in the later case (when no id is provided) i want only one record to be returned. Is there a way to do so ? do i have to redisign the db schema ?

thanx
theodore