What are different types of relational constraints?

  1. Domain constraints

  2. Key constraints

  3. Entity integrity constraints

  4. Referential integrity constraints

Domain constraints specify that the value of each attribute must be an atomic value from the domain of the attributes.

Key constraints tell that no two tuples can have the same combination of values for all their attributes.

Entity integrity constraint states that no primary key value can be null.

Referential integrity constraints states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation it is specified between two relations and is used to maintain the consistency among tuples of the two relations.