1
GATE CSE 2012
MCQ (Single Correct Answer)
+1
-0.3
Given the basic $$ER$$ and relational models, which of the following is INCORRECT?
A
An attribute of an entity can have more than one value
B
An attribute of an entity can be composite
C
In a row of a relational table, an attribute can have more than one value
D
In a row of a relational table, an attribute can have exactly one value or a NULL value
2
GATE CSE 2012
MCQ (Single Correct Answer)
+1
-0.3
Which of the following is TRUE?
A
Every relation in $$3NF$$ is also in $$BCNF$$
B
A relation $$R$$ is in $$3NF$$ if every non-prime attribute of $$R$$ is fully functionally dependent on every key of $$R$$
C
Every relation in $$BCNF$$ is also in $$3NF$$
D
No relation can be in both $$BCNF$$ and $$3NF$$
3
GATE CSE 2012
MCQ (Single Correct Answer)
+1
-0.3
Which of the following statements are TRUE about an SQL query?

P: An SQL query can contain a HAVING clause even if it does not have a GROUP BY clause
Q: An SQL query can contain a HAVING clause only if it has a GROUP BY clause
R: All attributes used in the GROUP BY clause must appear in the SELECT clause
S: Not all attributes used in the GROUP BY clause need to appear in the SELECT clause

A
P and R
B
P and S
C
Q and R
D
Q and S
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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