...
Process-Scheduling
December 13, 2023
Question 13095 – HCU PHD CS MAY 2014
December 13, 2023
Process-Scheduling
December 13, 2023
Question 13095 – HCU PHD CS MAY 2014
December 13, 2023

UGC NET CS 2016 July- paper-2

Question 20
Consider the following database table having A, B, C and D as its four attributes and four possible candidate keys (I, II,III and IV) for this table :

I : {B}
II : {B, C}
III : {A, D}
IV : {C, D}
If different symbols stand for different values in the table (e.g., d​1​ is definitely not equal to d​2​ ), then which of the above could not be the candidate key for the database table ?
A
I and III only
B
III and IV only
C
II only
D
I only
Question 20 Explanation: 
→Given table will find that attribute {B},{A,D},{C,D} can uniquely identify each tuple of the given table.
→ So, we can say that {B},{A,D},{C,D} are the candidate keys of the given relation. And we know that a candidate key is a minimal key using which each tuple of a relation can be uniquely identified
And the super set of a candidate key is a Super Key instead of candidate Key.
→ Since {B} is a candidate key so {B,C} is a Super Key, not the Candidate key of the given relation.
→ So, the key which can’t be the candidate key of given relation is {B,C}.
Correct Answer: C
Question 20 Explanation: 
→Given table will find that attribute {B},{A,D},{C,D} can uniquely identify each tuple of the given table.
→ So, we can say that {B},{A,D},{C,D} are the candidate keys of the given relation. And we know that a candidate key is a minimal key using which each tuple of a relation can be uniquely identified
And the super set of a candidate key is a Super Key instead of candidate Key.
→ Since {B} is a candidate key so {B,C} is a Super Key, not the Candidate key of the given relation.
→ So, the key which can’t be the candidate key of given relation is {B,C}.

Leave a Reply

Your email address will not be published. Required fields are marked *