Data integrity in relational databases is ensured through a combination of methods that help maintain the accuracy, consistency, and reliability of data. These methods include the use of constraints, transactions, and normalization. Each of these plays a key role in preventing data anomalies and ensuring the database operates as intended.
One primary way to enforce data integrity is through constraints, which are rules applied to the database schema. Common constraints include primary keys, foreign keys, unique constraints, and check constraints. A primary key is used to uniquely identify each record in a table, preventing duplicate entries, while foreign keys establish a relationship between tables, ensuring referential integrity. For example, if a Customer table has a primary key of CustomerID, and an Order table includes a CustomerID as a foreign key, the database will not allow an order to be placed for a customer that does not exist. This prevents orphan records and maintains a logical structure throughout the database.
Transactions are another vital aspect of ensuring data integrity. They allow multiple database operations to be executed as a single unit, which helps avoid partial updates that could lead to inconsistency. If any part of a transaction fails, the entire transaction can be rolled back, restoring the database to its previous state. For instance, if a transaction is intended to transfer funds from one bank account to another, both the debit and credit operations must succeed. If the credit operation fails after the debit has been processed, the database can roll back the debit, preventing incorrect balances. This atomicity of transactions plays an essential role in preserving the overall integrity of data in a relational database.