Integrity constraints

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Integrity constraints are used to ensure accuracy and consistency of data in a relational database.^{[citation needed]}

Types

Codd initially defined two sets of constraints but, in his second version of the relational model, he came up with four integrity constraints: ^{[citation needed]}

Entity Integrity

For more details on this topic, see Entity integrity.

The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation. Having null value for the primary key implies that we cannot identify some tuples.This also specifies that there may not be any duplicate entries in primary key column key word.

Referential Integrity

For more details on this topic, see Referential integrity.

The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuples in the two relations. Informally, the referential integrity constraint states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation. It is a rule that maintains consistency among the rows of the two relations in dbms.

Domain Integrity

Domain constraints allows us to test the values inserted into the database and to test the queries to make sure comparisons made are appropriate.

User Defined Integrity

A business rule is a statement that defines or constrains some aspect of the business. It is intended to assert business structure or to control or influence the behavior of the business. E.g.: Age>=18 && Age<=60

References

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