Integrity Constraints

Integrity constraints are a set of rules. It is used to maintain the quality of

information.

o Integrity constraints ensure that the data insertion, updating, and other

processes have to be performed in such a way that data integrity is not

affected.

o Thus, integrity constraint is used to guard against accidental damage to the

database.

Types of Integrity Constraint



1. Domain constraints

o Domain constraints can be defined as the definition of a valid set of values

for an attribute.

o The data type of domain includes string, character, integer, time, date,

currency, etc. The value of the attribute must be available in the

corresponding domain.

2. Entity integrity constraints

o The entity integrity constraint states that primary key value can't be null.

o This is because the primary key value is used to identify individual rows in

relation and if the primary key has a null value, then we can't identify those

rows.

o A table can contain a null value other than the primary key field.


3. Referential Integrity Constraints

o A referential integrity constraint is specified between two tables.

o In the Referential integrity constraints, if a foreign key in Table 1 refers to the

Primary Key of Table 2, then every value of the Foreign Key in Table 1 must

be null or be available in Table 2.


4. Key constraints

o Keys are the entity set that is used to identify an entity within its entity set

uniquely.

o An entity set can have multiple keys, but out of which one key will be the

primary key. A primary key can contain a unique and null value in the

relational table.