This set of Database Multiple Choice Questions & Answers [MCQs] focuses on “Functional-Dependency Theory”.
1. We can use the following three rules to find logically implied functional dependencies. This collection of rules is called
a] Axioms
b] Armstrong’s axioms
c] Armstrong
d] Closure
View Answer
Answer: b
Explanation: By applying these rules repeatedly, we can find all of F+, given F.
2. Which of the following is not Armstrong’s Axiom?
a] Reflexivity rule
b] Transitivity rule
c] Pseudotransitivity rule
d] Augmentation rule
View Answer
Answer: c
Explanation: It is possible to use Armstrong’s axioms to prove that Pseudotransitivity rule is sound.
3. The relation employee[ID,name,street,Credit,street,city,salary] is decomposed into
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employee1 [ID, name] employee2 [name, street, city, salary]
This type of decomposition is called
a] Lossless decomposition
b] Lossless-join decomposition
c] All of the mentioned
d] None of the mentioned
View Answer
Answer: d
Explanation: Lossy-join decomposition is the decomposition used here .
Check this: RDBMS MCQ | Programming Books
4. Inst_dept [ID, name, salary, dept name, building, budget] is decomposed into
instructor [ID, name, dept name, salary] department [dept name, building, budget]
This comes under
a] Lossy-join decomposition
b] Lossy decomposition
c] Lossless-join decomposition
d] Both Lossy and Lossy-join decomposition
View Answer
Answer: d
Explanation: Lossy-join decomposition is the decomposition used here .
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5. There are two functional dependencies with the same set of attributes on the left side of the arrow:
A->BC
A->B
This can be combined as
a] A->BC
b] A->B
c] B->C
d] None of the mentioned
View Answer
Answer: a
Explanation: This can be computed as the canonical cover.
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6. Consider a relation R[A,B,C,D,E] with the following functional dependencies:
ABC -> DE and D -> AB
The number of superkeys of R is:
a] 2
b] 7
c] 10
d] 12
View Answer
Answer: c
Explanation: A superkey is a combination of columns that uniquely identifies any row within a relational database management system [RDBMS] table.
7. Suppose we wish to find the ID’s of the employees that are managed by people who are managed by the employee with ID 123. Here are two possible queries:
I.SELECT ee.empID FROM Emps ee, Emps ff WHERE ee.mgrID = ff.empID AND ff.mgrID = 123; II.SELECT empID FROM Emps WHERE mgrID IN [SELECT empID FROM Emps WHERE mgrID = 123];
Which, if any, of the two queries above will correctly [in SQL2] get the desired set of employee ID’s?
a] Both I and II
b] I only
c] II only
d] Neither I nor I
View Answer
Answer: a
Explanation: The query can be satisfied by any of the two options.
8. Suppose relation R[A,B] currently has tuples {[1,2], [1,3], [3,4]} and relation S[B,C] currently has {[2,5], [4,6], [7,8]}. Then the number of tuples in the result of the SQL query:
SELECT * FROM R NATURAL OUTER JOIN S; IS:
a] 2
b] 4
c] 6
d] None of the mentioned
View Answer
Answer: a
Explanation: The SQL NATURAL JOIN is a type of EQUI JOIN and is structured in such a way that, columns with same name of associate tables will appear once only.
9. Suppose now that R[A,B] and S[A,B] are two relations with r and s tuples, respectively [again, not necessarily distinct]. If m is the number of [not necessarily distinct] tuples in the result of the SQL query:
R intersect S;
Then which of the following is the most restrictive, correct condition on the value of m?
a] m = min[r,s]
b] 0 E
Which of the following is not a key?
a] A
b] E
c] B, C
d] D
View Answer
Answer: c
Explanation: Here the keys are not formed by B and C.
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