Keys in Relational Databases

Two rows in the Student table both say Rahul Sharma, both in Computer Science, both in the second year.

A support ticket asks you to drop one of them from a course. Which one?

There is no answer, because nothing in the table separates the two rows. A key is what makes the answer exist.

This lesson defines seven kinds of key. Read it slowly. Chapter 6 and chapter 7 state their rules in exactly these words, and a fuzzy definition here becomes a wrong answer there.

Superkey

A superkey is a set of attributes whose values are different in every row.

More exactly: `K