What database value represents "unknown"?

The value that represents "unknown" in a database context is null. In databases, a null value signifies the absence of any value or a non-applicable situation; it indicates that no data is available for a specific column in a row. This distinguishes it from other data types, as null does not equate to zero, an empty string, or any other value; it specifically indicates that the value is unset or not defined.

Utilizing null values is important for accurately representing real-world scenarios where data might not always be available or relevant. For example, in a customer database, if a customer has not provided an email address, it would be appropriate to store this as a null rather than a blank string or an arbitrary placeholder. This helps maintain data integrity and provides clearer insights during data analysis.

In contrast to null, intermediate entity, parent key, and primary key have specific meanings and purposes within a database schema. An intermediate entity typically describes a relationship between two other entities in a many-to-many relationship, a parent key refers to the unique identifier in a one-to-many relationship, and a primary key uniquely identifies each record in a table. None of these concepts represent the idea of having an unknown or unset value.