GATE CSE 2021 Set 2 Q16: Foreign keys: how many per relation, and self-reference

Consider the following statements S1 and S2 about the relational data model:

S1: A relation scheme can have at most one foreign key.

S2: A foreign key in a relation scheme R cannot be used to refer to tuples of R.

Which one of the following choices is correct?

Try it: multiple choice: exactly one correct option

Wrong answer costs 1/3 mark in GATE.

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Answer: D (official GATE 2021 final answer key)

Concept used: A relation may have several foreign keys, and a foreign key may refer to the same relation (self-referencing).

First step: Think of emp(empId, managerId, deptId): managerId refers to emp itself and deptId refers to dept.

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Source: official GATE 2021 Set 2 CS question paper and final answer key, organised by IIT Bombay. Question paper · Answer key