The following table has two attributes A and C where A is the primary key and C is the foreign key referencing A with on-delete cascade.

A   C
-----
4   6
5   6
6   5
7   4
9   4
11  7
8   6 

The set of all tuples that must be additionally deleted to preserve referential integrity when the tuple (4,6) is deleted is:
(A) (5,6), (6,5) and (8,6)
(B) (5,6) and (8,6)
(C) (7,4) and (9,4)
(D) (7,4), (9,4) and (11,7)


Answer: (D)

Explanation: When (4,6) is deleted. Since C is a foreign key referring A with delete on cascade, all entries with value 4 in C must be deleted. So (7, 4) and (9, 4) are deleted. As a result of this 7 and 9 are deleted from A which causes (11, 7) to be deleted.

So, option (D) is correct.

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