Question 8149 – Operating-Systems
December 13, 2023Question 13095 – HCU PHD CS MAY 2014
December 13, 2023Database-Management-System
| Question 652 |
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., d1 is definitely not equal to d2 ), then which of the above could not be the candidate key for the database table ?
I : {B}
II : {B, C}
III : {A, D}
IV : {C, D}
If different symbols stand for different values in the table (e.g., d1 is definitely not equal to d2 ), then which of the above could not be the candidate key for the database table ?
| I and III only | |
| III and IV only | |
| II only | |
| I only |
Question 652 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}.
→ 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 652 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}.
→ 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}.
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