Database Systems MCQ

 Q.1 When R∩S = Ф , then the cost of computing R|><|S is

(A) the same as R × S

(B) greater the R × S

(C) less than R × S

(D) cannot say anything

Ans: (A)

 

Q.2 In SQL the word ‘natural’ can be used with

(A) inner join

(B) full outer join

(C) right outer join

(D) all of the above

Ans: (A)

 

Q.3 The default level of consistency in SQL is

(A) repeatable read

(B) read committed

(C) read uncommitted

(D) serializable

Ans: (D)

 

Q.4 If a transaction T has obtained an exclusive lock on item Q, then T can

(A) read Q

(B) write Q

(C) both read and write Q

(D) write Q but not read Q

Ans: (C)

 

Q.5 Shadow paging has

(A) no redo

(B) no undo

(C) redo but no undo

(D) neither redo nor undo

Ans: (A)

 

Q.6 If the closure of an attribute set is the entire relation then the attribute set is a

(A) superkey

(B) candidate key

(C) primary key

(D) not a key

Ans: (A)

 

Q.7 DROP is a ______________ statement in SQL.

(A) Query

(B) Embedded SQL

(C) DDL

(D) DCL

Ans: (C)

 

Q.8 If two relations R and S are joined, then the non matching tuples of both R and S are ignored in

(A) left outer join

(B) right outer join

(C) full outer join

(D) inner join

Ans: (D)

 

Q.9 The keyword to eliminate duplicate rows from the query result in SQL is

(A) DISTINCT

(B) NO DUPLICATE

(C) UNIQUE

(D) None of the above

Ans: (C)

 

Q.10 In 2NF

(A) No functional dependencies (FDs) exist.

(B) No multivalued dependencies (MVDs) exist.

(C) No partial FDs exist.

(D) No partial MVDs exist.

Ans: (C)

 

Q.11 Which one is correct statement?

Logical data independence provides following without changing application programs:

(i) Changes in access methods.

(ii) Adding new entities in database

(iii) Splitting an existing record into two or more records

(iv) Changing storage medium

(A) (i) and (ii) (B) (iv) only, (C) (i) and (iv) (D) (ii) and (iii)

Ans: (D)

 

Q.12 In an E-R, Y is the dominant entity and X is a subordinate entity. Then which of the following is incorrect :

(A) Operationally, if Y is deleted, so is X

(B) existence is dependent on Y.

(C) Operationally, if X is deleted, so is Y.

(D) Operationally, if X is deleted, & remains the same.

Ans: (C)

 

Q.13 Relational Algebra is

(A) Data Definition Language .

(B) Meta Language

(C) Procedural query Language

(D) None of the above

Ans: (C)

 

Q.14 Which of the following aggregate functions does not ignore nulls in its results?.

(A) COUNT .

(B) COUNT (*)

(C) MAX

(D) MIN

Ans: (B)

 

Q.15 R (A,B,C,D) is a relation. Which of the following does not have a lossless join dependency preserving BCNF decomposition

(A) A->B, B->CD

(B) A->B, B->C, C->D .

(C) AB->C, C->AD

(D) A->BCD

Ans: (D)

 

Q.16 Consider the join of relation R with a relation S. If R has m tuples and S has n tuples, then the maximum and minimum size of the join respectively are

(A) m+n and 0

(B) m+n and |m-n|

(C) mn and 0

(D) mn and m+n

Ans: (C)

 

Q.17 Maximum height of a B+ tree of order m with n key values is

(A) Log_m(n)

(B) (m+n)/2

(C) Log_m/2(m+n)

(D) None of these

Ans: (D)

 

Q.18 Which one is true statement :

(A) With finer degree of granularity of locking a high degree of concurrency is possible.

(B) Locking prevents non – serializable schedules.

(C) Locking cannot take place at field level.

(D) An exclusive lock on data item X is granted even if a shared lock is already held on X.

Ans: (A)

 

Q.19 Which of the following statement on the view concept in SQL is invalid?

(A) All views are not updateable

(B) The views may be referenced in an SQL statement whenever tables are referenced.

(C) The views are instantiated at the time they are referenced and not when they are defined.

(D) The definition of a view should not have GROUP BY clause in it.

Ans: (D)

 

Q.20 Which of the following concurrency control schemes is not based on the serializability property?

(A) Two – phase locking

(B) Graph-based locking

(C) Time-stamp based locking

(D) None of these

Ans: (D)

 

Q.21 Which of the following is a reason to model data?

(A) Understand each user’s perspective of data

(B) Understand the data itself irrespective of the physical representation

(C) Understand the use of data across application areas

(D) All of the above

Ans: (D)

 

Q.22 If an entity can belong to only one lower level entity then the constraint is

(A) disjoint

(B) partial

(C) overlapping

(D) single

Ans: (B)

 

Q.23 The common column is eliminated in

(A) theta join

(B) outer join

(C) natural join

(D) composed join

Ans: (C )

 

Q.24 In SQL, testing whether a subquery is empty is done using

(A) DISTINCT

(B) UNIQUE

(C) NULL

(D) EXISTS

Ans: (D)

 

Q.25 Use of UNIQUE while defining an attribute of a table in SQL means that the attribute

values are

(A) distinct values

(B) cannot have NULL

(C) both (A) & (B)

(D) same as primary key

Ans: (C)