Need help with sql statement

I have a form that contains 6 checkboxes. I need my sql statement to be able to handle the combination of selected checkboxes.

I am having trouble writing my sql to accept any combination of selected checkboxes.

Right now I have this:

Select SystemNetName From Host
Where
(Site = location1 OR
Site = location2 OR
Site = location3 ) OR
UseType = usetype1 OR
UseType = usetype2 OR
UseType = usetype3) AND
Active_Inactive = active

This sql statement does not accomodate for empty 'None' in any of these fields. Ideally, it should work like this: IF I leave one of the checkboxes blank it should not try to query it as an empty field.

Any Suggestions?
-Laura