![Functional Dependency](/wp-content/uploads/2022/12/FD.png)
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
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