It would help if you showed the query you are trying to build and told us a
little bit about the type of fields you are applying the criteria against.

SELECT Field1
FROM SomeTable
WHERE Field2 = Forms![NameOfForm]![NameOfComboSource]

If Field2 always has a value and is always text you can use:
SELECT Field1
FROM SomeTable
WHERE Field2 LIKE Nz(Forms![NameOfForm]![NameOfComboSource],"*")

Otherwise you can use
SELECT Field1
FROM SomeTable
WHERE Field2 = Forms![NameOfForm]![NameOfComboSource]
OR Forms![NameOfForm]![NameOfComboSource] Is Null


John Spencer
Access MVP 2002-2005, 2007-2009
The Hilltop Institute
University of Maryland Baltimore County

Proko wrote:
I am having a problem with the iif statement when I use it in the criteria
for a query for a combo box (Combo2) that is based on the selection of
another combo box (Combo1)

Essentially, what I am trying to do is show all choices in combo2 if there
has not been a selection in Combo1; And show a filtered selection in Combo2
if there is a selection in Combo1.

I am trying to do this using the iif statement when setting the criteria in
the Combo2 query.

iif (isnull(combo1), No Criteria is Set, Criteria is set)

I am having trouble with the "No Criteria is Set" part of the expression.
Leaving it blank, inserting Null or "" (zero length string" doesn't work.

Why am I doing this? Not only do I want to be able to make a selection in
Combo1 then a selection in Combo2 based on Combo1's selection but I want to
be able to do it the other way round. ie make a selection in Combo2 (so I
need all choices displayed) which will automatically make a selection in
Combo1.

I hope all this makes sense.

Is there a way? Or am I going about this the wrong way.

Any help would be greatly appreciated.

Thanks