> ## Documentation Index
> Fetch the complete documentation index at: https://axiom.co/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Null values

> This page explains how APL represents missing values.

All scalar data types in APL have a special value that represents a missing value. This value is called the null value, or null.

## Null literals

The null value of a scalar type D is represented in the query language by the null literal D(null). The following query returns a single row full of null values:

```kusto theme={null}
print bool(null), datetime(null), dynamic(null), int(null), long(null), real(null), double(null), time(null)
```

## Predicates on null values

The scalar function [isnull()](/apl/scalar-functions/string-functions#isnull\(\)) can be used to determine if a scalar value is the null value. The corresponding function [isnotnull()](/apl/scalar-functions/string-functions#isnotnull\(\)) can be used to determine if a scalar value isn’t the null value.

## Equality and inequality of null values

* Equality (`==`): Applying the equality operator to two null values yields `bool(null)`. Applying the equality operator to a null value and a non-null value yields `bool(false)`.
* inequality(`!=`): Applying the inequality operator to two null values yields `bool(null)`. Applying the inequality operator to a null value and a non-null value yields `bool(true)`.