## Functional Dependency

- Functional Dependency (FD) is a relationship that exists between attributes.
- It exists between primary key & non-key attribute in a table

X -> Y

LHS is called Determinant

RHS is called Dependent

**Example** Emp_ID -> Emp_Address

Here Emp_Address is functional dependent on Emp_ID

- FD helps to maintain the quality of data in DB
- It help to find difference between good & bad design of database

**Types of Functional Dependency**

- Trivial Functional Dependency (TFD)
- Non-trivial Functional Dependency (FD)

**1) Trivial FD**

i) A->B has trivial functional dependency if B is a subset of A

ii) A->A & B->B is also Trivial Functional Dependency (TFD)

**2) Non-Trivial FD**

If B is not subset of A

When A intersection B(A n B) is null, then A->B is called as complete non-trivial functional dependency

**Example**

ID -> Name

Name -> Address/DOB

**UGC NET EXAM Questions**

**Q1)** Consider a relation R(A,B,C,D,E) with the following functional dependencies

ABC -> DE and

D -> AB

**Solution**

The number of superkeys of R is 10

Superkey is a combination of columns that uniquely identifies any row within RDBMS table

**Q2)** Suppose relation R(A,B,C,D,E) has the following functional dependencies

A->B

B->C

BC->A

A->D

E->A

D->E

Which of the following is not a key?

**Solution:** B,C

Here the keys are not formed by B & C

**Q3)** If E is a set of Functional Dependency then closure of E is denoted by?

**Solution:** E+

**Q4)** If A->B, A->C then which of the following is true?

**Solution**

- A->BC
- A->B
- A->C
**All are true**

**Q5)** If B is an attribute & A->B then B is said to be ____________________________ by A.

**Solution:** Functionally Determined