Microsoft Access VBA Tip: Use the NZ() NullToZero Function to Handle Null Values

Behavior of Null Values in Equations (Expressions)

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, Microsoft Access offers a way around this issue in VBA module code or 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).

Example for Using the NZ Function

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.

Syntax for NZ Function

Definition

Nz(Value, ValueIfNull)

Parameters

There are two parameters. The second one is optional and lets you override the default value for nulls. For instance, you may want Nulls to be treated as 1, or for text fields, a zero-length string ("") rather than zero.

Parameter	Required or Optional	Data Type	Description
Value	Required	Variant	Value to evaluate for Null
ValueIfNull	Optional	Variant	The custom return value if the value being evaluated is Null (overrides the default value)

Return Value

If the Value parameter is not null, the Value is returned.
If the Value parameter is null:
- If the ValueIfNull parameter is provided, ValueIfNull
- If the ValueIfNull parameter is not provided, a zero (0) or zero-length string ("").
  Note that when used in a query expression, the NZ function returns a zero-length string.

Check out the VBA help file for the complete definition of the NZ function.

Additional Resource and Limitations of NZ Function

On a related note, read our whitepaper Microsoft Access Query Sorting on Multiple Date or Numeric Fields with Blank (Null) Values where we discuss how the Immediate If command (IIF) is used to choose which field to sort and behaves differently from using the NZ function.

Note that the Nz Function is a Microsoft Access VBA function and does not exist in Visual Basic 6 (VB6) or other Office VBA environments.