The Relational Model: Null Values

In the relational model used by PostgreSQL, null values represent missing or unknown information within a database. Unlike zero, empty strings, or other default values, null signifies the absence of a value and is treated uniquely in operations and queries. For example, any arithmetic operation involving a null results in a null, and comparisons with null using standard operators return unknown rather than true or false. To handle null values, PostgreSQL provides specific functions and constructs such as IS NULL, IS NOT NULL, and the COALESCE function, which returns the first non-null value in its arguments. Understanding and correctly handling null values is crucial for accurate data retrieval and integrity in relational databases.