Using NullToZero Nz() VBA Function in
expressions to generate correct results with Nulls
Provided by: FMS Development Team
Any arithmetic calculation in VBA with a Null value results
in a null value. If one of the values is NULL, the result is Null (blank).
According to VBA rules for calculating values, the result is null because a
null value is an unknown. Nulls are not the same value as zero (0).
However, in many situations that's exactly what we want. We
want to treat Nulls as zeros.
Thankfully, VBA offers a way around this issue which can be
used in code or Access queries. The NullToZero function (NZ) takes a null
value and converts it to zero. You should use this function anywhere a value
could be null (like a field that is not required).
The following can be used to calculate the sum of two fields
in the query:
Nz([Field1]) + Nz([Field2])
If [Field1] is null and [Field2] is 2, the result is 2.
Without the Nz() function, the result would be null. So be safe! Wrap your
potential null values with NZ.
Check out the VBA help file for the complete definition of
the NZ function. You can add a second parameter for a non-zero value for
nulls (for instance, you may want Nulls to be treated as 1).