42. Foreign key

DBMS Published 30 Sept 2026 Updated 30 Sept 2026 0 Views Verified

Create orders so customer_id must reference an existing customer.

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Answer & Explanation

4 Answers

Verified Correct Answer

Option A

CREATE TABLE orders (id BIGINT PRIMARY KEY, customer_id BIGINT NOT NULL, FOREIGN KEY (customer_id) REFERENCES customers(id));

Additional Explanation

Correct implementation. Prefer parameterized queries in application code, validate affected rows for UPDATE/DELETE, and use transactions for related writes.

Verified

Option B

CHECK (customer_id IN customers);

Additional Explanation

This option is incorrect for the stated requirement.

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Option C

FOREIGN KEY (customer_id) REFERENCES customers(name);

Additional Explanation

This option is incorrect for the stated requirement.

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Option D

UNIQUE (customer_id) REFERENCES customers(id);

Additional Explanation

This option is incorrect for the stated requirement.