In a database, what is the difference betwen a key and an index?

Question

For example, in SQLServer, if I have an index with \'unique\' set on it, how is that different from a key?

How do I know when I want to use a Key vs. an Indexed field?

Answer 1

Keys are used to maintain data integrity, indexes are used to maintain database performance. Think about whatever problem you're trying to solve and that will lead you in the right direction.