A table can have multiple candidate keys but only a single primary key. If the subset of the candidate key is a super key, then that candidate key is not a valid candidate key. Therefore, the foreign key cannot contain values that do not appear in the table that it refers to. Primary key is the minimal super keys. Now, today we are going to discuss two very important keys of DBMS i.e. Difference between Candidate Key vs Primary Key:- ) Both Primary and Candidate keys can uniquely identify records in a table on database. Only one Candidate Key can be Primary Key.

Primary Key – A Primary Key is a column or a combination of columns that uniquely identify a record. One needs to be very careful in selecting the Primary Key as an incorrect selection can adversely impact the database architect and future normalization. Only those super keys would become a candidate key which have no redundant attributes. Every table must have at least a single candidate key.
Primary Key: It is a candidate key that is chosen by the database designer to identify entities with in an entity set. Therefore, keys help to establish the relationships between tables. Within a given link, a collection of one or more attributes having values that sure are unique within a connection.

The foreign key or the columns in the referencing table must be the primary key or a candidate key (a key that can be used as the primary key) in the referenced table.

Candidate Key is a super key with no repeated attributes.

What is a Candidate Key? 3) Primary key or Candidate keys can be either single column or combination of multiple columns in a table. Only one Candidate Key can be Primary Key. In other words candidate keys are minimal super keys. Candidate Keys Candidate Keys are super keys for which no proper subset is a super key. The Primary key should be selected from the candidate keys. 2) Both Primary and Candidate keys are has constraints UNIQUE and NOT NULL. Primary key and Foreign key, and we will also discuss the difference between primary key and foreign key. CANDIDATE KEY is a set of attributes that uniquely identify tuples in a table.

The primary key is the candidate key that is selected by the data architect and defined as a primary key constraint in a table definition. It is a good practice to define a primary key for every table and to always use the primary key to relate to a row in a table with a foreign key constraint. Example: In the above example, we had 6 super keys but all of them cannot become a candidate key. the primary key in SQL, Candidate key, Alternate key, Foreign key | keys in DBMS The primary key in SQL (DBMS Primary key) A primary key is a set of one or more attributes that can uniquely identify tuples within the relation.

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