A new café ordering database allows orders to be entered even when the customer ID does not exist in the customer table. Later, reports show orphaned orders that cannot be tied to real customers. Which database control would have best prevented this?

Question

BlackTom AI · Accepted Answer

Referential integrity via a foreign-key constraint ensures every order.customer_id corresponds to an existing customer.customer_id.

1) Relevant knowledge points and concepts
- Referential (relational) integrity: a database rule that enforces relationships between tables so foreign key values must match primary key values in the referenced table.
- Foreign key constraint: the implementation of referential integrity in relational databases.
- Orphaned records: rows in a child table (orders) that reference non‑existent parent rows (customers).

2) Step-by-step reasoning
- The problem: orders were entered with customer IDs that do not exist in the customer table, producing orphaned orders.
- What would block that at write time? A foreign-key constraint on orders.customer_id referencing customers.customer_id.
- How it works practically: when an INSERT or UPDATE tries to set orders.customer_id to a value not present in customers.customer_id, the DBMS rejects the operation with a constraint violation.
- Additional behavior: the constraint can also prevent deleting a customer row if dependent orders exist (or require cascade/delete rules), so it keeps the database consistent.

3) Intermediate demonstration (SQL example)
- ALTER TABLE orders ADD CONSTRAINT fk_orders_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id);
- Attempting INSERT INTO orders (order_id, customer_id, ...) VALUES (123, 999, ...) will fail if customer_id 999 is not in customers.

4) Why the correct answer is correct
- A "relational integrity constraint requiring valid customer IDs" directly enforces the necessary rule at the database level and prevents orphaned orders from being created.

5) Why the other options are incorrect
- Hot-site configuration: a disaster recovery capability for uptime/continuity, not data validation.
- Business continuity plan: organizational planning for operations during disruptions, not a data integrity control.
- Multi-tenancy for the reporting environment: an architecture choice for isolated tenants; it does not enforce referential integrity or prevent orphaned records.

Conclusion: A relational integrity constraint requiring valid customer IDs is the correct control and matches the provided answer.

A new café ordering database allows orders to be entered even when the customer ID does not exist in the customer table. Later, reports show orphaned orders that cannot be tied to real customers. Which database control would have best prevented this?单项选择题

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