updateanomalie

Updateanomalie (update anomaly) is a data integrity problem that can arise in a database table when the same fact is stored in multiple rows or fields, making updates error-prone. It occurs in unnormalized or denormalized relations where redundancy exists. When a value changes, all occurrences must be updated to keep data consistent; if any are overlooked, the database can contain conflicting values.

A classic example involves a table that records products and their suppliers with repeated supplier data. Suppose a single supplier supplies many products, and the SupplierName and SupplierAddress are stored in each product row. If the supplier moves, updating the address requires updating every product row referencing that supplier. Failing to update all rows yields inconsistent data.

Update anomalies are often seen together with other anomalies when data is not properly normalized, such as insert anomalies (inserting a row may require duplicating data) and delete anomalies (removing data may remove information about a supplier that still has other products). They can complicate maintenance and undermine data integrity.

Mitigation relies on database normalization. By decomposing into separate relations (for example, a Suppliers table and a Products table with a foreign key to Suppliers), redundancy is reduced and updates become localized to a single place. Higher normal forms (2NF, 3NF, BCNF) and clear keys help prevent update anomalies, at the cost of more complex queries or joins. In modern databases, update anomalies are less common due to normalized schemas, though controlled denormalization may be used for performance reasons.