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

Key has by default a cluster index in MS SQL Server.

Key is unique value for each row.

Index use to maximize your database performance. You can create indexes according to your requirement. there are different kind of indexes e.g.

• Bitmap index
• Dense index
• Sparse index
• Covering Index