# What is a candidate key in functional dependencies?

## What is a candidate key in functional dependencies?

Candidate Key is minimal set of attributes of a relation which can be used to identify a tuple uniquely. For Example, each tuple of EMPLOYEE relation given in Table 1 can be uniquely identified by E-ID and it is minimal as well. So it will be Candidate key of the relation.

### How do you get a candidate key from functional dependencies?

A candidate key is a minimal superkey. In other words, there are no superflous attributes in the key. The first step to finding a candidate key, is to find all the superkeys. For those unfamiliar, a super key is a set of attributes whose closure is the set of all atributes.

**What will be the candidate key for relation R having functional dependencies F?**

Therefore BD is the candidate key. Example-2: A relation R(ABCDE) is given with functional dependencies F: { A→BC, CD→E, B→D, E→A }.

**How do you find the candidate key in a relationship?**

- The first step in the process of finding a normal form and decomposing a relation is to find the candidate. keys.
- R = (ABCDE), F = {A -> C, E -> D, B -> C}
- R = ABCDE, F = {A -> BE, C -> BE, B -> D}
- R = ABCDEF, F = {A -> B, B -> D, C -> D, E -> F}
- R = ABCD, F={AB -> C, BC -> D, CD -> A}
- R = ABCD, F={A -> BCD, C -> A}

## Which of the following is candidate key?

Candidate Key is a Super Key whose no proper subset is a super key, i.e. suppose if ABC is a candidate key then neither A, B, C or any of its combination can be super key, hence we can say candidate key is a minimal set of attributes of an R( Relational Schema) which can be used to identify a tuple of a table uniquely.

### Is primary key a candidate key?

Primary key is a Candidate key chosen to uniquely identify tuples in the table. Primary key values should be unique and non-null. There can be multiple Super keys and Candidate keys in a table, but there can be only one Primary key in a table.

**What is a candidate key give an 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 are the candidate keys for R explain?**

## What is candidate key example?

### How do you create 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.

**What is candidate key and super key?**

Super Key is an attribute (or set of attributes) that is used to uniquely identifies all attributes in a relation. Candidate Key is a subset of a super key. In a relation, number of super keys are more than number of candidate keys. While in a relation, number of candidate keys are less than number of super keys.

**What is super key candidate key and primary key?**

Super Key – A super key is a group of single or multiple keys which identifies rows in a table. Primary Key – is a column or group of columns in a table that uniquely identify every row in that table. Candidate Key – is a set of attributes that uniquely identify tuples in a table.

## What is an example of a functional dependency?

Example:. A relation R (ABCD) is given with functional dependencies F: { AB→CD, D→A }. Find out the candidate keys of the sub relation R’ (BCD). {B}+ = B, cant derive all the attributes present in the sub relation i.e BCD, so its not a candidate key.

### What are the superkeys of the functional dependencies?

Since we have the functional dependencies: A -> B, BC -> E, and ED -> A, we have the following superkeys: ACD (We can get B through A -> B, and then we can get E through BC -> E) (One trick here to realize, is that since C and D never appear on the right side of a functional dependency, every key must include both C and D)

**Which attributes are not present on RHS of any functional dependency?**

Here, the attributes which are not present on RHS of any functional dependency are A, C and F. The remaining attributes of the relation are non-essential attributes. This is because they can be determined by using essential attributes. If all essential attributes together can determine all remaining non-essential attributes, then-

**Which attribute is a candidate key?**

No other set of attributes is a candidate key, since the only other attribute on the left side is A, but GA is determined by G, so it can be eliminated from that dependency. Thanks for contributing an answer to Database Administrators Stack Exchange!