Q

Difference between candidate key and composite key

What is the difference between candidate key and composite key?

What is the difference between candidate key and composite key?

We've been getting a number of this type of question lately: short, and simple on the surface. Short questions...

are wonderful, because they leave more room for the answer. Simple questions are even better, as long as they aren't too simple.

In this case, it's a good question but it might have been too simple.

A candidate key is any key that could be used as the primary key. This comes with two requirements: it cannot be null, and its values must be unique.

A composite key contains more than one column.

This was last published in April 2007

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