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Entity Integrity Constraint:
It states that in a relation no attribute of a primary key (K) can have a null value. If a K consists of a single attribute, this constraint obviously applies on this attribute, so it cannot have the Null value. However, if a K consists of multiple attributes, then none of the attributes of this K can have the Null value in any of the instances.
Referential Integrity Constraint :
This constraint is applied to foreign keys. Foreign key is an attribute or attribute combination of a relation that is the primary key of another relation. This constraint states that if a foreign key exists in a relation, either the foreign key value must match the primary key value of some tuple in its home relation or the foreign key value must be completely null.