Top 100 DBMS Questions and Answers

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Database Interview Questions

1. Which of the following key is required to handle the data when the encryption is applied to the data so that the unauthorized user cannot access the data?

a) Primary key

b) Authorised key

c) Encryption key

d) Decryption key

Answer: d

2. Which of the following is known as the process of viewing cross-tab with a fixed value of one attribute?

a) Dicing

b) Pivoting

c) Slicing

d) Both Pivoting and Dicing

Answer: c

3. For designing a normal RDBMS which of the following normal form is considered adequate?

a) 4NF

b) 3NF

c) 2NF

d) 5NF

Answer: b

4. Which of the following is popular for applications such as storage of log files in a database management system since it offers the best write performance?

a) RAID level 0

b) RAID level 1

c) RAID level 2

d) RAID level 3

Answer: b

5. Which of the following represents a query in the tuple relational calculus?

a) { }{P(t) | t }

b) {t | P(t)}

c) t | P() | t

d) All of the mentioned

Answer: b

6. The oldest DB model is _______________

a) Network

b) Physical

c) Hierarchical

d) Relational

Answer: a

7. Which of the following establishes a top-to-bottom relationship among the items?

a) Relational schema

b) Network schema

c) Hierarchical schema

d) All of the mentioned

Answer: c

8. A major goal of the db system is to minimize the number of block transfers between the disk and memory. Which of the following helps in achieving this goal?

a) Secondary storage

b) Storage

c) Catalog

d) Buffer

Answer: d

9. What happens if a piece of data is stored in two places in the db?

a) Storage space is wasted & Changing the data in one spot will cause data inconsistency

b) In can be more easily accessed

c) Changing the data in one spot will cause data inconsistency

d) Storage space is wasted

Answer: a

10. The logical design, and the snapshot of the data at a given instant in time is known as?

a) Instance & Relation

b) Relation & Schema

c) Domain & Schema

d) Schema & Instance

Answer: d

11. A relational database consists of a collection of

a) Tables

b) Fields

c) Records

d) Keys

Answer: a

12. A ________ in a table represents a relationship among a set of values.

a) Column

b) Key

c) Row

d) Entry

Answer: c

13. The term _______ is used to refer to a row.

a) Attribute

b) Tuple

c) Field

d) Instance

Answer: b

14. The term attribute refers to a ___________ of a table.

a) Record

b) Column

c) Tuple

d) Key

Answer: b

15. For each attribute of a relation, there is a set of permitted values, called the ________ of that attribute.

a) Domain

b) Relation

c) Set

d) Schema

Answer: a

16. Database __________ which is the logical design of the database, and the database _______ which is a snapshot of the data in the database at a given instant in time.

a) Instance, Schema

b) Relation, Schema

c) Relation, Domain

d) Schema, Instance

Answer: d

17. A domain is atomic if elements of the domain are considered to be ____________ units.

a) Different

b) Indivisbile

c) Constant

d) Divisible

Answer: b

18. The tuples of the relations can be of ________ order.

a) Any

b) Same

c) Sorted

d) Constant

Answer: a

19. Which one of the following is a set of one or more attributes taken collectively to uniquely identify a record?

a) Candidate key

b) Sub key

c) Super key

d) Foreign key

Answer: c

20. Consider attributes ID, CITY and NAME. Which one of this can be considered as a super key?

a) NAME

b) ID

c) CITY

d) CITY, ID

Answer: b

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DBMS Interview Questions

1. The subset of a super key is a candidate key under what condition?

a) No proper subset is a super key

b) All subsets are super keys

c) Subset is a super key

d) Each subset is a super key

Answer: a

2. A _____ is a property of the entire relation, rather than of the individual tuples in which each tuple is unique.

a) Rows

b) Key

c) Attribute

d) Fields

Answer: b

3. Which one of the following attribute can be taken as a primary key?

a) Name

b) Street

c) Id

d) Department

Answer: c

4. Which one of the following cannot be taken as a primary key?

a) Id

b) Register number

c) Dept_id

d) Street

Answer: d

5. An attribute in a relation is a foreign key if the _______ key from one relation is used as an attribute in that relation.

a) Candidate

b) Primary

c) Super

d) Sub

Answer: b

6. The relation with the attribute which is the primary key is referenced in another relation. The relation which has the attribute as a primary key is called ______________

a) Referential relation

b) Referencing relation

c) Referenced relation

d) Referred relation

Answer: c

7. The ______ is the one in which the primary key of one relation is used as a normal attribute in another relation.

a) Referential relation

b) Referencing relation

c) Referenced relation

d) Referred relation

Answer: c

8. A _________ integrity constraint requires that the values appearing in specified attributes of any tuple in the referencing relation also appear in specified attributes of at least one tuple in the referenced relation.

a) Referential

b) Referencing

c) Specific

d) Primary

Answer: a

9. Using which language can a user request information from a database?

a) Query

b) Relational

c) Structural

d) Compiler

Answer: a

10. Which one of the following is a procedural language?

a) Domain relational calculus

b) Tuple relational calculus

c) Relational algebra

d) Query language

Answer: c

11. The_____ operation allows the combining of two relations by merging pairs of tuples, one from each relation, into a single tuple.

a) Select

b) Join

c) Union

d) Intersection

Answer: b

12. The result which operation contains all pairs of tuples from the two relations, regardless of whether their attribute values match.

a) Join

b) Cartesian product

c) Intersection

d) Set difference

Answer: b

13. The _______operation performs a set union of two “similarly structured” tables

a) Union

b) Join

c) Product

d) Intersect

Answer: a

14. The most commonly used operation in relational algebra for projecting a set of tuple from a relation is

a) Join

b) Projection

c) Select

d) Union

Answer: c

15. The _______ operator takes the results of two queries and returns only rows that appear in both result sets.

a) Union

b) Intersect

c) Difference

d) Projection

Answer: b

16. A ________ is a pictorial depiction of the schema of a database that shows the relations in the database, their attributes, and primary keys and foreign keys.

a) Schema diagram

b) Relational algebra

c) Database diagram

d) Schema flow

Answer: a

17. The _________ provides a set of operations that take one or more relations as input and return a relation as an output.

a) Schematic representation

b) Relational algebra

c) Scheme diagram

d) Relation flow

Answer: b

18. Which one of the following is used to define the structure of the relation, deleting relations and relating schemas?

a) DML(Data Manipulation Langauge)

b) DDL(Data Definition Langauge)

c) Query

d) Relational Schema

Answer: b

19. Which one of the following provides the ability to query information from the database and to insert tuples into, delete tuples from, and modify tuples in the database?

a) DML(Data Manipulation Langauge)

b) DDL(Data Definition Langauge)

c) Query

d) Relational Schema

Answer: a

20. The basic data type char(n) is a _____ length character string and varchar(n) is _____ length character.

a) Fixed, equal

b) Equal, variable

c) Fixed, variable

d) Variable, equal

Answer: c

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DBMS MCQs

1. To remove a relation from an SQL database, we use the ______ command.

a) Delete

b) Purge

c) Remove

d) Drop table

Answer: d

2. Updates that violate __________ are disallowed.

a) Integrity constraints

b) Transaction control

c) Authorization

d) DDL constraints

Answer: a

3. The ______ clause allows us to select only those rows in the result relation of the ____ clause that satisfy a specified predicate.

a) Where, from

b) From, select

c) Select, from

d) From, where

Answer: a

4. The ________ clause is used to list the attributes desired in the result of a query.

a) Where

b) Select

c) From

d) Distinct

Answer: b

5. Which of the following statements contains an error?

a) Select * from emp where empid = 10003;

b) Select empid from emp where empid = 10006;

c) Select empid from emp;

d) Select empid where empid = 1009 and lastname = ‘GELLER’;

Answer: d

6. In SQL the spaces at the end of the string are removed by _______ function.

a) Upper

b) String

c) Trim

d) Lower

Answer: c

7. _____ operator is used for appending two strings.

a) &

b) %

c) ||

d) _

Answer: c

8. The union operation is represented by

a) ∩

b) U

c) –

d) *

Answer: b

9. The intersection operator is used to get the _____ tuples.

a) Different

b) Common

c) All

d) Repeating

Answer: b

10. The union operation automatically __________ unlike the select clause.

a) Adds tuples

b) Eliminates unique tuples

c) Adds common tuples

d) Eliminates duplicate

Answer: d

11. If we want to retain all duplicates, we must write ________ in place of union.

a) Union all

b) Union some

c) Intersect all

d) Intersect some

Answer: a

12. The number of attributes in relation is called as its

a) Cardinality

b) Degree

c) Tuples

d) Entity

Answer: b

13. _____ clause is an additional filter that is applied to the result.

a) Select

b) Group-by

c) Having

d) Order by

Answer: c

14. _________ joins are SQL server default

a) Outer

b) Inner

c) Equi

d) None of the mentioned

Answer: b

15. The _____________ is essentially used to search for patterns in target string.

a) Like Predicate

b) Null Predicate

c) In Predicate

d) Out Predicate

Answer: a

16. A _____ indicates an absent value that may exist but be unknown or that may not exist at all.

a) Empty tuple

b) New value

c) Null value

d) Old value

Answer: c

17. If the attribute phone number is included in the relation all the values need not be entered into the phone number column. This type of entry is given as

a) 0

b) –

c) Null

d) Empty space

Answer: c

18. The predicate in a where clause can involve Boolean operations such as and. The result of true and unknown is_______ false and unknown is _____ while unknown and unknown is _____

a) Unknown, unknown, false

b) True, false, unknown

c) True, unknown, unknown

d) Unknown, false, unknown

Answer: d

19. In an employee table to include the attributes whose value always have some value which of the following constraint must be used?

a) Null

b) Not null

c) Unique

d) Distinct

Answer: b

20. Using the ______ clause retains only one copy of such identical tuples.

a) Null

b) Unique

c) Not null

d) Distinct

Answer: d

DBMS Viva Questions

1. The primary key must be

a) Unique

b) Not null

c) Both Unique and Not null

d) Either Unique or Not null

Answer: c

2. The result of _____unknown is unknown.

a) Xor

b) Or

c) And

d) Not

Answer: d

3. Aggregate functions are functions that take a ___________ as input and return a single value.

a) Collection of values

b) Single value

c) Aggregate value

d) Both Collection of values & Single value

Answer: a

4. All aggregate functions except _____ ignore null values in their input collection.

a) Count(attribute)

b) Count(*)

c) Avg

d) Sum

Answer: b

5. A Boolean data type that can take values true, false, and________

a) 1

b) 0

c) Null

d) Unknown

Answer: d

6. The ____ connective tests for set membership, where the set is a collection of values produced by a select clause. The ____ connective tests for the absence of set membership.

a) Or, in

b) Not in, in

c) In, not in

d) In, or

Answer: c

7. The phrase “greater than at least one” is represented in SQL by _____

a) < all

b) < some

c) > all

d) > some

Answer: d

8. We can test for the nonexistence of tuples in a subquery by using the _____ construct.

a) Not exist

b) Not exists

c) Exists

d) Exist

Answer: b

9. SQL applies predicates in the _______ clause after groups have been formed, so aggregate functions may be used.

a) Group by

b) With

c) Where

d) Having

Answer: b

10. Aggregate functions can be used in the select list or the_______clause of a select statement or subquery. They cannot be used in a ______ clause.

a) Where, having

b) Having, where

c) Group by, having

d) Group by, where

Answer: b

11. The ________ keyword is used to access attributes of preceding tables or subqueries in the from clause.

a) In

b) Lateral

c) Having

d) With

Answer: b

12. Subqueries cannot:

a) Use group by or group functions

b) Retrieve data from a table different from the one in the outer query

c) Join tables

d) Appear in select, update, delete, insert statements.

Answer: c

13. Which of the following is not an aggregate function?

a) Avg

b) Sum

c) With

d) Min

Answer: c

14. The EXISTS keyword will be true if:

a) Any row in the subquery meets the condition only

b) All rows in the subquery fail the condition only

c) Both of these two conditions are met

d) Neither of these two conditions is met

Answer: a

15. How can you find rows that do not match some specified condition?

a) EXISTS

b) Double use of NOT EXISTS

c) NOT EXISTS

d) None of the mentioned

Answer: b

16. A Delete command operates on ______ relation.

a) One

b) Two

c) Several

d) Null

Answer: a

17. Which one of the following deletes all the entries but keeps the structure of the relation.

a) Delete from r where P;

b) Delete from instructor where dept name= ’Finance’;

c) Delete from instructor where salary between 13000 and 15000;

d) Delete from instructor;

Answer: d

18. _________ are useful in SQL update statements, where they can be used in the set clause.

a) Multiple queries

b) Sub queries

c) Update

d) Scalar subqueries

Answer: d

19. The problem of ordering the update in multiple updates is avoided using

a) Set

b) Where

c) Case

d) When

Answer: c

20. The____condition allows a general predicate over the relations being joined.

a) On

b) Using

c) Set

d) Where

Answer: a

Top 100 DBMS Questions and Answers