What is candidate key with example?

What is candidate key with example?

Candidate Key: The minimal set of attributes that can uniquely identify a tuple is known as a candidate key. For Example, STUD_NO in STUDENT relation. The value of the Candidate Key is unique and non-null for every tuple. There can be more than one candidate key in a relation.

What is the meaning of candidate key?

A candidate key is a set of attributes (or attribute) which uniquely identify the tuples in relation or table. As we know that Primary key is a minimal super key, so there is one and only one primary key in any relationship but there is more than one candidate key can take place.

What is the difference between a candidate key and primary key?

Primary Key is a unique and non-null key which identify a record uniquely in table. Candidate key is also a unique key to identify a record uniquely in a table but a table can have multiple candidate keys.

How do you write a candidate key?

You declare a column as a candidate key by using the keyword UNIQUE . Precede the UNIQUE keyword with the NOT NULL specification. Like a primary key, a candidate key also uniquely identifies a row in a table. Note that a table can have only one primary key, but can have any number of candidate keys.

Is a/b a candidate key?

We have to consider all the relations that might be assigned to a relvar to determine whether a certain set of attributes is a candidate key. For example, if we had considered only r1 then we would have concluded that {A,B} is a candidate key, which is incorrect.

What is the purpose of a candidate key?

Candidate key means exactly the same thing as primary key. All candidate keys serve the same purpose: to ensure data integrity by preventing duplicate data. It’s perfectly sensible for a table to have more than one candidate key enforced in it if that’s necessary to ensure some data is not duplicated.

Can a candidate key be a primary key?

Each Candidate Key can qualify as Primary Key. Primary Key – A Primary Key is a column or a combination of columns that uniquely identify a record. Only one Candidate Key can be Primary Key.

Why candidate key is required?

All candidate keys serve the same purpose: to ensure data integrity by preventing duplicate data. It’s perfectly sensible for a table to have more than one candidate key enforced in it if that’s necessary to ensure some data is not duplicated.

Can a relation have no candidate key?

Every relation without NULL values will have at least one candidate key: Since there cannot be duplicate rows, the set of all columns is a superkey, and if that isn’t minimal, some subset of that will be minimal. …

What is the difference between a candidate key and a superkey?

The main difference between super key and candidate key is that the super key is a set of one or more attributes that can uniquely identify a record in a table, while the candidate key is a super key that does not contain any redundant attributes .

What are some examples of candidate keys?

Candidate Key Example {Emp_Id} – No redundant attributes {Emp_Number} – No redundant attributes {Emp_Id, Emp_Number} – Redundant attribute. {Emp_Id, Emp_Name} – Redundant attribute Emp_Name. {Emp_Id, Emp_Number, Emp_Name} – Redundant attributes. {Emp_Number, Emp_Name} – Redundant attribute Emp_Name.

What is difference between candidate key and alternate key?

A candidate key are those keys which are unique means these are the candidate for primary key of table while An alternate key is a set of candidate key which are not primary keys in table. Candidate Key -Candidate keys are those which is unique,i.e.

What is the difference between candidate key and composite key?

The main difference between candidate key and composite key is that candidate key is a super key with no redundant attributes while the composite key is a key with two or many attributes to identify the rows of the table. Generally, a database in an RDBMS has tables to store data. The keys help to create a relationship between the tables.