Which referential Integrity enforcement option would you select if you want to prevent a user from deleting a record in a parent table (e.g., Customer) as long as it is still referenced by records in a child table (e.g., Orders)?

Question

BlackTom AI · Accepted Answer

Restrict prevents deleting a parent record while child records still reference it, so the database will block the delete attempt until those child rows are removed or updated.

1) Relevant knowledge points and concepts
- Referential integrity ensures foreign key relationships remain consistent between parent and child tables.
- Common enforcement actions for ON DELETE (or ON UPDATE) are CASCADE, RESTRICT (or NO ACTION), and SET NULL.
- Behavior definitions: CASCADE deletes dependent child rows automatically; SET NULL changes the child foreign key to NULL; RESTRICT prevents the delete if any child rows exist.

2) Step-by-step reasoning process
- You have a Customer table (parent) and an Orders table (child) with Orders.CustomerID referencing Customer.ID.
- If a user attempts to delete Customer.ID = 123 while Orders contains rows with CustomerID = 123, the referential action determines what happens.
- Under RESTRICT, the DBMS checks for existing child rows and stops the delete, returning an error. The parent row remains.
- Under CASCADE, the DBMS would delete all Orders rows with CustomerID = 123 and then delete the Customer row.
- Under SET NULL, the DBMS would set Orders.CustomerID to NULL for those rows, then allow deletion of the Customer row.

3) Calculations
- No numerical calculations are required for this logical decision; the steps above show the operational checks the DBMS performs.

4) Why the correct answer is correct
- RESTRICT enforces that no parent row can be removed while child rows reference it, exactly matching the requirement to prevent deletion as long as references exist.

5) Why the other options are incorrect
- CASCADE is incorrect because it would remove the child Orders automatically (contrary to preventing deletion).
- SET-TO-NULL is incorrect because it would break the reference by nullifying the foreign key rather than preventing the deletion.

6) Conclusion
- Therefore, the appropriate referential integrity enforcement option is Restrict, which matches the provided correct answer.

Which referential Integrity enforcement option would you select if you want to prevent a user from deleting a record in a parent table (e.g., Customer) as long as it is still referenced by records in a child table (e.g., Orders)?单项选择题

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