What is referential integrity in a relational database?

Referential integrity in a relational database ensures that relationships between tables remain consistent and data is not corrupted.

In more detail, referential integrity is a fundamental aspect of data integrity in a relational database management system (RDBMS). It is a set of rules that RDBMS enforces to maintain the logical consistency and accuracy of the data. These rules ensure that the relationships between the tables in the database always hold true and that the data remains reliable and valid.

The concept of referential integrity revolves around the idea of foreign keys. A foreign key in one table points to a primary key in another table, creating a link or relationship between the two tables. For instance, in a school database, a 'Student' table might have a 'ClassID' foreign key that points to the 'ClassID' primary key in a 'Class' table. This relationship allows the database to understand which class a student belongs to.

Referential integrity rules stipulate that any foreign key value can be either a null value or should match exactly one of the primary key values from its parent table. This means that if a record in the 'Class' table is deleted, any students in the 'Student' table associated with that class must also be deleted or updated to reflect the change. Similarly, if a new student is added to the 'Student' table, the 'ClassID' must correspond to an existing class in the 'Class' table.

These rules prevent the occurrence of orphan records, which are records that do not correspond to any existing record in the parent table. Orphan records can lead to inaccurate data and misleading results when querying the database. By enforcing referential integrity, the database ensures that all data is consistent, accurate, and reliable.

In summary, referential integrity is a crucial aspect of maintaining data integrity in a relational database. It ensures that the relationships between tables are always consistent, preventing data corruption and enhancing the reliability of the database.