In database management systems (DBMS), a candidate key is a set of one or more columns that can be used to uniquely identify a row within a table. It is also known as a "unique identifier" or "primary key". A candidate key is a minimal set of attributes that can uniquely identify a tuple. It must contain unique values and cannot contain null values. Every table must have at least one candidate key, and a table can have multiple candidate keys but only one primary key. The primary key is used as the official unique identifier for a row within the table. The value of a candidate key is unique and may be null for a tuple. The candidate key can be simple (having only one attribute) or composite (having multiple attributes) .

Candidate keys play a vital role in maintaining the integrity and consistency of a database. They ensure that each row within a table is unique and can be identified independently, allowing for accurate data retrieval and preventing data duplication. The purpose of a candidate key is to specify the uniqueness of a database record. Although a primary key already specifies uniqueness, a table can have more than one candidate key, and specifying additional candidate keys can help to ensure data integrity.

In summary, a candidate key is a set of one or more columns that can uniquely identify a row within a table. It is a minimal set of attributes that must contain unique values and cannot contain null values. Every table must have at least one candidate key, and a table can have multiple candidate keys but only one primary key. Candidate keys play a vital role in maintaining the integrity and consistency of a database by ensuring that each row within a table is unique and can be identified independently.