Aug2016 cs Q18

0. Consider the following statements regarding relational database model:
(a) NULL values can be used to opt a tuple out of enforcement of a foreign key.
(b) Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.
(c) The difference between the project operator (Π) in relational algebra and the SELECT keyword in SQL is that if the resulting table/set has more than one occurrences of the same tuple, then Π will return only one of them, while SQL SELECT will return all.
One can determine that:

Answer
Comment
Array

Option : D
Explanation :
In relational database model:
(a) NULL values can be used to opt a tuple out of enforcement of a foreign key. Correct
(b) Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF. Correct
(c) The difference between the project operator (Π) in relational algebra and the SELECT keyword in SQL is that if the resulting table/set has more than one occurrences of the same tuple, then Π will return only one of them, while SQL SELECT will return all. Correct
So, option (D) is correct.

Forgot your password?

I agree with the Terms.