Which approach enforces referential integrity in a relational database?

• A. Data type constraints on keys
• B. Foreign key constraints that reference primary keys with on update/delete actions as needed
• C. Indexing all columns
• D. Trigger-based replication of data across tables

Answer: (B)

Referential integrity means that a value in a foreign key must correspond to an existing value in the related table’s primary key, so you don’t end up with references to nowhere. The reliable way to enforce this is to declare a foreign key constraint that points to the primary key of the parent table and define how updates or deletes should be handled (for example, cascade, restrict, or set null). This built-in mechanism automatically prevents inserting invalid foreign keys and keeps related rows in sync when changes occur, ensuring the relationship remains valid across both tables.

Data type constraints on keys help ensure the values have the right type, but they don’t enforce the cross-table link between a child row and its parent row. Indexing all columns improves query performance but does not enforce referential links. Trigger-based replication or checks can enforce rules in some cases, but they’re not as reliable or centralized for maintaining core relationships as foreign key constraints with defined update/delete actions.