All Primary keys are definitely Candidate Keys. A Candidate key is one which can be used as a Primary key that is not null and unique. That is one of the candidate keys can be chosen as a primary key.A Candidate key is a Unique Key and it can be used to find out any particular Tuple (row) in a table.

The following are the differences between A Candidate key and a Primary Key:

1) A Unique key can be null but not a Primary key

2) On a table we can have only 1 primary key but 'N' number of unique keys.

more than one primary key to identify the record uniquely is called candidate key.

Candidate Key is used to uniquely identify the records of a table. An attribute becomes a Primary Key, if all the other candidate keys lose race for being qualified as Primary Key.

We designate one of the candidate key of a relation to be a primary key because that primary key is use for any foreign key references.

A candidate key is a unique key that can uniquely identify each record in a database table, whereas a secondary key is a non-unique key used for data retrieval and indexing purposes. Candidate keys can be chosen as the primary key for the table, while secondary keys provide alternate ways to access and organize the data.