nullwert

Nullwert (null value) is a term used in mathematics, statistics, and information technology to denote the absence of a value for a variable, field, or data item. It is not the same as zero, an empty string, or a placeholder; its meaning depends on the context and the conventions of the system in which it appears.

In databases and SQL, NULL indicates that a value is unknown or not applicable. It is not equal to zero or to an empty value, and comparisons with NULL generally yield an unknown result. SQL provides special constructs such as IS NULL and IS NOT NULL to test for null values, and arithmetic or concatenation with NULL typically yields NULL.

In programming languages, a null value often takes the form of a null reference or null pointer that points to no object. Attempting to access members of a null value can cause runtime errors; languages differ in how they represent and enforce null safety. Some languages offer optional types or explicit checks to reduce null-related errors.

In data collection and measurement, a Nullwert signals missing data rather than a numeric zero. How such values are treated—whether omitted, imputed, or coded with a separate missing-value category—depends on the analysis.

Handling null values requires clear documentation of semantics and consistent treatment across datasets and applications. Proper use of null values helps distinguish between the absence of information and a legitimate numeric value.

See also: Null value, Null pointer, Missing data.