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August 26, 2024Relational-databases
| Question 6 |
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:
(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:
| (a) and (b) are true. | |
| (a) and (b) are true | |
| (b) and (c) are true | |
| (a), (b) and (c) are true |
Question 6 Explanation:
Option(A) is correct. NULL values can be used to opt a tuple out of enforcement of a foreign key.
Option(B) is correct. Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.
Option (C) is correct because the main difference between Project operator and SELECT keyword is that SELECT keyword will return Duplicate values if the exist in the result of a query but Project Operator Do not return Duplicate values if the exist in the result of the query.
Option(B) is correct. Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.
Option (C) is correct because the main difference between Project operator and SELECT keyword is that SELECT keyword will return Duplicate values if the exist in the result of a query but Project Operator Do not return Duplicate values if the exist in the result of the query.
Correct Answer: D
Question 6 Explanation:
Option(A) is correct. NULL values can be used to opt a tuple out of enforcement of a foreign key.
Option(B) is correct. Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.
Option (C) is correct because the main difference between Project operator and SELECT keyword is that SELECT keyword will return Duplicate values if the exist in the result of a query but Project Operator Do not return Duplicate values if the exist in the result of the query.
Option(B) is correct. Suppose that table T has only one candidate key. If Q is in 3NF, then it is also in BCNF.
Option (C) is correct because the main difference between Project operator and SELECT keyword is that SELECT keyword will return Duplicate values if the exist in the result of a query but Project Operator Do not return Duplicate values if the exist in the result of the query.
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