Help constructing a query

[lauren quantrell]

I have a table of contacts tblCon that includes customers and sales
persons with the identity column ConID
I have a table tblLinks that contains links between contacts. It looks
like this:
ID Customer Salesman
1 123 678
2 456 901
3 789 901
where 123, 456, 789, 678, 901 are the ConID from tblCon. Salemen can be
assigned to more than one customer and customers can have more than one
salesman.

What I want to do is to create a contact detail form that includes a
combobox.
I want to populate the combobox so that when you open the combo box, it
is populated only with customers or salesmen which are not already
linked to the contact being viewed. For example, I open contact details
for salesman 901 and the combo box would only include customer 123
because 901 is already linked to 456 and 789.
The combobox has to consider that 901 may not yet be linked to any
customers and that it may be linked already to other customers that are
irrelevant.
I thought this was easy, and maybe it is, but I spent a lot of time
trying to construct this without success.

[pietlinden]

<snip>
What I want to do is to create a contact detail form that includes a
combobox.
I want to populate the combobox so that when you open the combo box, it
is populated only with customers or salesmen which are not already
linked to the contact being viewed.
</snip>

Can't you do that with a left join?

SELECT ...
FROM Contacts LEFT JOIN Salesmen ON ...
WHERE ContactID IS NULL

or something along those lines? Or are you trying to union the two
sets together? If that's the case, you'd have one left join query for
each set and then just UNION [ALL] to create one result set.

Or did I misunderstand the question?

if you can only populate the combo with Contacts XOR Salesmen, then I
would have another combo that set the rowsource of the one in question
through code.

Not sure if my reading of your question is right, but I hope this at
least points you in the right direction...