Not NULL Constraints

Last updated Dec 14, 2021 Edit Source

• Cs databases
• Cs theory

Because of the fact that a relation is defined as $R \subseteq D_1 \times D_2 … \times D_n$, and a tuple(which represents a relation) cannot have empty elements, We assume that a special NULL value is part of every domain. When we don’t want an element to be NULL, we give it the NOT NULL constraint. Keep in mind that Primary Key Constraints also automatically have NOT NULL constraints.