NULL type¶

The null value represents the absence of a value. It is different from an empty string, the number 0, or an empty container. NebulaGraph Database Developer Edition uses the NULL type during expression type inference when a null value does not yet have a specific material type.

The NULL type is an immaterial value type and cannot be used as a node or edge property type.

View the NULL type¶

Use the typeof() function to view the type of a NULL expression:

RETURN typeof(NULL)

Return:

+--------------+
| typeof(NULL) |
+--------------+
| NULL         |
+--------------+

NULL type, null value, and nullability¶

Concept	Example	Meaning
`NULL` type	`typeof(NULL)`	The type inferred for a standalone `NULL` expression when no more specific type can be determined from the context
Null value	`name = NULL`	Indicates that no value is currently present
Nullable type	`name STRING DEFAULT NULL`	The storage location permits a null value
Non-nullable type	`id INT64 NOT NULL`	The storage location does not permit a null value

For example:

'''
VALUE name STRING = NULL
RETURN typeof(name), name
'''

+--------------+------+
| typeof(name) | name |
+--------------+------+
| STRING       | null |
+--------------+------+

The declared type of name is STRING, and its current value is NULL. A null value does not change the declared type of a variable or property to NULL.

The same distinction applies to properties:

NODE Person (
  LABEL Person {
    id INT64 NOT NULL,
    name STRING DEFAULT NULL,
    PRIMARY KEY (id)
  }
)

The type of the name property is STRING, and DEFAULT NULL specifies its default value. You cannot declare a property as name NULL.

Uses of the NULL type¶

The NULL type is primarily used for expression type inference. A standalone NULL expression does not contain enough information to determine whether it represents a string, number, or date. When it is used in a context with a specific type, the system handles the null value according to that context.

NULL can also occur in container expressions such as lists, sets, and maps. When a container also contains non-null values, the system uses those values to infer the container element type.

Related operations¶

To test whether a value is null, see NULL predicate.
For null comparison rules, see Comparison predicates.
For null conversion rules, see Cast value expression.
For how functions handle null values, see Null behavior of functions.

Note

Use IS NULL or IS NOT NULL to test for a null value. Do not use an ordinary equality comparison.