Test by Bikram | Databases | Test 2 | Question: 24

Question

Consider the relation schemas:

Rank (name, rank) and student (name, country), where name in student table is a foreign key in table Rank.

Which of the following TRC Queries displays all the student names from India along with their respective ranks?

• A. $\{ t \mid \exists q \in Rank ( q [name] = t [name] \wedge  t [rank] = q [rank] ) \wedge \exists p \in student (q [name] = p [name] \wedge q [country] = " India ") \}$
• B. $\{ t \mid \exists p \in Rank ( t [name] = p [name] \wedge t [rank] = p [rank] ) \wedge \exists q \in student (p [name] = q [name] \wedge p [country] = " India ") \}$
• C. $\{ t \mid \exists p \in Rank ( p [name] = t [name] \wedge  p [rank] = q [rank] ) \wedge  \exists q \in student (q [name] = p [name] \wedge q [country] = " India ") \}$
• D.  $\{ t \mid \exists p \in Rank ( t [name] = p [name] \wedge  t [rank] = p [rank] ) \wedge  \exists q \in student (q [name] = p [name] \wedge q [country] = " India ")\}$

Comments

yes sir, now it is perfectly fine..

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Option A specifies $p$ as the variable for $student$, but accesses the attribute $country$ with $q$.

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Option B does the same — uses $p$ to access $country$, when it should've used $q$

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Option C accesses $rank$ with $q$ — which is out of $q$'s bounds. Same as above two

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Although it is not hard to guess but don’t you think that the variable “t” should have been explicitly associated with the table “Rank” to make the question more clear ?

Answer 1

option D will be answer......

Comments

@akash.dinkar12 why not C??

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@Jason

why u think C should be correct?

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c will only print t.name, it will not print t.rank