What is the uniqueness and role of a key in data structures or databases?

A key in a data structure or database is a unique record identifier that ensures unambiguous identification of each row.

The uniqueness of a key allows:

• Fast data retrieval and access.
• Ensuring data integrity by preventing duplication.
• Linking tables through foreign keys.

For example, in a user database, the key could be user_id — a unique number that can quickly provide information about a specific user.