1
GATE CSE 2015 Set 2
MCQ (Single Correct Answer)
+2
-0.6
Consider two relations $${R_1}\left( {A,B} \right)$$ with the tuples $$(1,5), (3,7)$$ and $${R_2}\left( {A,C} \right) = \left( {1,7} \right),\left( {4,9} \right).$$
Assume that $$R(A,B,C)$$ is the full natural outer join of $${R_1}$$ and $${R_2}$$. Consider the following tuples of the form $$(A,B,C): a = (1,5,null),$$ $$b = (1,null,7),$$ $$c = (3, null, 9),$$ $$d = (4,7,null),$$ $$e = (1,5,7),$$ $$f = (3,7,null),$$ $$g = (4,null,9).$$ Which one of the following statements is correct?
A
$$R$$ contains $$a, b, e, f, g$$ but not $$c, d.$$
B
$$R$$ contains all of $$a, b, c, d, e, f, g.$$
C
$$R$$ contains $$e, f, g$$ but not $$a, b.$$
D
$$R$$ contains $$e$$ but not $$f, g.$$
2
GATE CSE 2014 Set 2
MCQ (Single Correct Answer)
+2
-0.6
Consider a join (relation algebra) between relations r(R)and s(S) using the nested loop method. There are 3 buffers each of size equal to disk block size, out of which one buffer is reserved for intermediate results. Assuming size(r(R)) < size(s(S)), the join will have fewer number of disk block accesses if
A
relation r(R) is in the outer loop.
B
relation s(S) is in the outer loop.
C
join selection factor between r(R) and s(S) is more than 0.5.
D
join selection factor between r(R) and s(S) is less than 0.5.
3
GATE CSE 2014 Set 3
MCQ (Single Correct Answer)
+2
-0.6
Consider the relational schema given below, where eId of the relation dependent is a foreign key referring to empId of the relation employee. Assume that every employee has at least one associated dependent in the dependent relation:

employee (empId, empName, empAge)

dependent (depId, eId, depName, depAge)

Consider the following relational algebra query: $$\Pi_{empId}\:(employee) - \Pi_{empId}\:(employee \bowtie_{(empId=eID) \wedge (empAge \leq depAge)} dependent)$$

The above query evaluates to the set of empIds of employees whose age is greater than that of

A
some dependent.
B
all dependents.
C
some of his/her dependents.
D
all of his/her dependents.
4
GATE CSE 2012
MCQ (Single Correct Answer)
+2
-0.6
Suppose R1 (A, B) and R2 (C, D) are two relation schemas. Let r1 and r2 be the corresponding relation instances. B is a foreign key that refers to C in R2. If data in r1 and r2 satisfy referential integrity constraints, which of the following is ALWAYS TRUE?
A
$$\prod_{B}(r_{1})- \prod _{C}(r_{2})= \varnothing$$
B
$$\prod_{C}(r_{2})- \prod _{B}(r_{1})= \varnothing$$
C
$$\prod_{B}(r_{1}) = \prod _{C}(r_{2})$$
D
$$\prod_{B}(r_{1}) - \prod _{C}(r_{2}) \neq \varnothing$$
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