Explain about data integrity.

q)Explain about data integrity.

Database integrity:
It means the correctness and consistency of data. It is another form of database protection.
Put simply, data integrity is the assurance that data is consistent and correct.
Data integrity is normally enforced in a database system by a series of integrity constraints or rules.
         Three types of integrity constraints are an inherent part of the relational data model: entity integrity, referential integrity

Entity integrity concerns the concept of a primary key. Entity integrity is an integrity rule which states that every table must have a primary key and that the column or columns chosen to be the primary key should be unique and not null. It means the primary key’s data must not be missing in table/s.
The entity integrity is a constraint on primary key value. It states that any attribute of a primary key cannot contain null value. If primary key contains null value, it is not possible to uniquely identify a record in a relation. Entity integrity ensures that it should be easy to identify each entity in the database.

Referential integrity concerns the concept of a foreign key. The referential integrity rule states that any foreign key value can only be in one of two states. The usual state of affairs is that the foreign key value refers to a primary key value of some table in the database. Occasionally, and this will depend on the rules of the business, a foreign key value can be null. In this case we are explicitly saying that either there is no relationship between the objects represented in the database or that this relationship is unknown.
Referential Integrity
Referential integrity ensures that the relationship between the primary key (in a referenced table) and the foreign key (in each of the referencing tables) is always maintained. The maintenance of this relationship means that:
  • A row in a referenced table cannot be deleted, nor can the primary key be changed, if a foreign key refers to the row. For example, you cannot delete a customer that has placed one or more orders.
  • A row cannot be added to a referencing table if the foreign key does not match the primary key of an existing row in the referenced table. For example, you cannot create an order for a customer that does not exist.

Domain Integrity
Domain (or column) integrity specifies the set of data values that are valid for a column and determines whether null values are allowed. Domain integrity is enforced by validity checking and by restricting the data type, format, or range of possible values allowed in a column.

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