Nullwerts

Nullwerts is a term used in German-speaking contexts to denote a null value, the absence of a known or applicable value in data. It is used in databases, programming, and mathematical contexts. A null value is not the same as zero, an empty string, or a false boolean; it signifies unknown or missing information.

In relational databases, NULL is the standard marker for a missing value. SQL uses a three-valued logic with TRUE, FALSE, and UNKNOWN; any comparison with NULL yields UNKNOWN. To test for missing values, predicates such as IS NULL and IS NOT NULL are used. To simplify processing, functions like COALESCE, NVL, or ISNULL replace NULL with a non-null value. Aggregate operations are affected by NULLs: many aggregates ignore NULLs, while COUNT(*) includes rows with NULLs in non-specified columns.

In programming languages, null references can lead to runtime errors known as null dereferences. Many languages provide mechanisms to mitigate this risk, such as optional types or null-safety features (for example, Java Optional, Kotlin null safety, Swift Optionals). These approaches encourage explicit handling of the absence of a value and often require defaulting, masking, or explicit absence types.

In mathematics, the idea of a missing or undefined value overlaps with, but is not identical to, concepts like NaN or undefined functions. The treatment of missing values depends on the formal system and the context of use.

Handling Nullwerts is a central concern in data quality and analysis, influencing data cleaning, reporting, and decision-making. Strategies include imputation, explicit metadata about data confidence, and robust data modeling.