Nullqry.mdb demonstrates a query which filters records by a lower
parameter and an upper parameter.  Two controls on a form are used 
to provide the parameters.

  The query returns recordsets based on the following conditions:

- If [Lower Parameter] is NULL then return all records less than 
	[Upper Parameter].
- If [Upper Parameter] is NULL then return all records greater than 
	[Lower Parameter].
- If both are NULL then return all records INCLUDING those where the
	filtered field is NULL.
- If neither are NULL then return all records between [Lower Parameter]
	and [Upper Parameter], (inclusively).

This sample database contains two such queries.  The first uses 
two parameters on one field, [Birthday].  The second query is an 
expanded, two-dimensional version using four parameters on [Longitude] 
and [Latitude].  This example uses +/- 90 for latitude values and 
+/- 180 for longitude values.

