SQL Foreign Keys MCQ Referential Integrity Practice Questions

Direction: Choose the correct option

What is the purpose of a foreign key?

A. Group data

B. Link two tables together

C. Sort data

D. Create index

Direction: Choose the correct option

CREATE TABLE orders (
    order_id INT PRIMARY KEY,
    customer_id INT,
    FOREIGN KEY (customer_id) REFERENCES customers(id)
);

What does customer_id reference?

A. customers table id column

B. customer_id column

C. customers table

D. orders table

Direction: Choose the correct option

What happens if you try to insert a foreign key value that doesn't exist in parent table?

A. Insert fails with error

B. Default value used

C. NULL is inserted

D. Insert succeeds

Direction: Choose the correct option

What does ON DELETE CASCADE do?

A. Prevents parent deletion

B. Deletes child rows when parent deleted

C. Sets child to NULL

D. Updates child rows

Direction: Choose the correct option

What does ON DELETE SET NULL do?

A. Sets foreign key to NULL when parent deleted

B. Sets parent to NULL

C. Deletes parent only

D. Prevents deletion

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