Practice mode DBMS and SQL

Table Student(roll_no, cnic, email, name) has roll_no, cnic and email each unique and never NULL. If roll_no is chosen as the primary key, what are cnic and email called?

Correct answer C. Alternate keys

Explanation

All three of roll_no, cnic and email are candidate keys, since each alone uniquely identifies a student. The designer chooses one, roll_no, as the primary key. The candidate keys that were not chosen are called alternate (secondary) keys and are usually enforced with UNIQUE constraints. They are not composite keys, because each consists of a single attribute.

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Table Student(roll_no, cnic, email, name) has roll_no, cnic and email each unique and never NULL. If roll_no is chosen as the primary key, what are cnic and email called?

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Table Student(roll_no, cnic, email, name) has roll_no, cnic and email each unique and never NULL. If roll_no is chosen as the primary key, what are cnic and email called?

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