Answer
Referential integrity means foreign-key references remain valid. • A referencing value must match a referenced key or be NULL when allowed. • Deleting or changing referenced rows follows the configured action. • The database enforces the relationship across statements and transactions.
💡 SQL Example
ALTER TABLE orders ADD CONSTRAINT orders_customer_fk FOREIGN KEY (customer_id) REFERENCES customers(customer_id);
Result
ALTER TABLE
⚡ Quick Revision
Referential integrity prevents invalid references between related tables.