DBMS Questions Gate 2005
Question 1 : Which one of the following is a key factor for
preferring B+trees to binary search trees for indexing
database relations?
a) Database relations have a large number of records
b) Database relations are sorted on the primary key
c) B+ trees require less memory than binary search trees
d) Data transfer from disks is in blocks
Solution : (d) is the correct option.
The transfer of data from disk to primary memory is in the
form of data blocks. If a data block is large, then
indexing is easy due to this B+ tree.It is better than
binary search tree if large amount of data can be access.
Question 2 : Which one of the following statements about normal forms
is FALSE?
a) BCNF is stricter than 3NF
b) Lossless, dependencypreserving decomposition into 3NF
is always possible
c) Lossless, dependencypreserving decomposition into BCNF
is always possible
d) Any relation with two attributes is in BCNF
Solution : (c) is the correct option. Check out the link for
explanation.
http://www.edugrabs.com/normalformsshortcutsforgatestudents/
Question 3 : Let r be a relation instance with schema
R = (A, B, C, D). We define r1 = ΠA, B, C (r) and
r2 = ΠA.D (r). Let s = r1 * r2 where * denotes natural
join. Given that the decomposition of r into r1 and r2
is lossy, which one of the following is TRUE?
a) s ⊂ r
b) r ∪ s
c) r ⊂ s
d) r * s = s
Solution :
Question 4 : Let E1 and E2 be two entities in an E/R diagram with
simple singlevalued attributes. R1 and R2 are two
relationships between E1 and E2, where R1 is onetomany
and R2 is manytomany. R1 and R2 do not have any
attributes of their own. What is the minimum number of
tables required to represent this situation in the
relational model?
a) 2
b) 3
c) 4
d) 5
Solution :
(b) is the right answer.
Question 5 : The following table has two attributes A and C where A is the
primary key and C is the foreign key referencing A with
on delete cascade.
A 
C 
2 
4 
3 
4 
4 
3 
5 
2 
7 
2 
9 
5 
6 
4 

The set of all tuples that must be additionally deleted to
preserve referential integrity when the tuple (2,4) is
deleted is:
a) (3,4) and (6,4)
b) (5,2) and (7,2)
c) (5,2), (7,2) and (9,5)
d) (3,4), (4,3) and (6,4)
Solution :
So, (c) is the right answer.
Question 6 : The relation book (title, price) contains the titles and
prices of different books. Assuming that no two books
have the same price, what does the following SQL query
list?
select title
from book as B
where (select count(*)
from book as T
where T.price > B.price) < 5
a) Titles of the four most expensive books
b) Title of the fifth most inexpensive book
c) Title of the fifth most expensive bookTitles of the
five most expensive books
d) Titles of the five most expensive books
Solution :
Question 7 : Consider a relation scheme R = (A, B, C, D, E, H) on
which the following functional dependencies hold:
{A–>B, BC–>D, E–>C, D–>A}.
What are the candidate keys of R?
a) AE, BE
b) AE, BE, DE
c) AEH, BEH, BCH
d) AEH, BEH, DEH
Solution :
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