Nullable
See also Null References - The Billion Dollar Mistake by Tony Hoare, Tony Hoare, Null (SQL), Null reference, Null pointer, Null pointer exception, Nullable type, Null-Safety
In databases, a nullable column is one that is allowed to store null values. This means that a record or a field in a column can have no value or be undefined, which is typically represented by a null value in most database management systems. The nullable constraint is important when designing database schemas, as it provides flexibility in data storage. Not all fields in a table require a value, and allowing null values ensures that incomplete or missing data can be handled appropriately. This is common in cases where data may not be available at the time of entry or when some attributes are optional.
https://en.wikipedia.org/wiki/Nullable
A nullable field in a database is defined at the time of table creation by setting the nullable attribute for a specific column. In contrast, a not nullable column requires every record in that column to have a value, and if a null value is attempted to be inserted, an error will occur. In many databases, fields are set to nullable by default unless explicitly defined otherwise. However, some databases allow you to define a column as not nullable during the schema creation to enforce data integrity and ensure that missing values are avoided in critical fields.
https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/NULL.html
The use of nullable fields plays an essential role in ensuring the accuracy of database operations, especially in databases that interact with incomplete or sparse data. Handling null values appropriately is crucial for preventing errors and ensuring that queries return the expected results. When designing queries or reports, developers must consider whether fields can have null values to ensure that the operations on these fields behave as intended. Moreover, nullable columns are essential in data modeling and database normalization processes, especially in situations where information may be missing or irrelevant for certain records.
https://www.sqlshack.com/sql-null-value-usage-in-sql-server/