About
Every data type includes a special value, called the null value, sometimes denoted by the keyword NULL that reflects the optionality character of the value.
The data type of the null value implied by the keyword NULL cannot be inferred since the null value is in every data type
Although the null value is neither equal to any other value nor not equal to any other value — it is unknown whether or not it is equal to any given value.
A null is the absence of a value in a column of a row. Nulls indicate missing, unknown, or inapplicable data. A null should not be used to imply any other value, such as zero.
Null is the representation of “missing information and inapplicable information”.
Language
Most programming languages use null as an absence of value. Ie the variable is not pointing to any value or object.
The meaning is implementation dependent and can represent the fact that:
- the data was not processed
- or the data is unknown
Character
There is even a null character.