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DBMS Questions

To crack the Interviews for various Computer and IT Sector jobs in TCS, Freshers as well as experience technicals must go through the top DBMS Interview Questions given in the following section of this page. You can also download free DBMS Interview Questions and Answers PDFs through the links given below.

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DBMS Interview Questions PDF

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DBMS Interview Questions

Here we have provided some commonly asked DBMS interview questions along with their specific answers. Concerned aspirants seeking jobs in IT and Computer Sector must check these DBMS Viva Questions and Answers in order to prepare for the interviews effectively.

DBMS Interview Questions with Answers:

1) What is DBMS used for?

Answer: DBMS, commonly known as Database Management System, is an application system whose main purpose revolves around the data. This is a system that allows its user to store the data, define it, retrieve it and update the information about the data inside the database.

2) What is meant by a Database?

Answer: In simple terms, Database is a collection of data in some organized way to facilitate its users to easily access, manage and upload the data.

3) Why is the use of DBMS recommended? Explain by listing some of its major advantages.

Answer: Some of the major advantages of DBMS are as follows:

Controlled Redundancy: DBMS supports a mechanism to control the redundancy of data inside the database by integrating all the data into a single database and as data is stored at only one place, the duplicity of data does not happen.

Data Sharing: Sharing of data among multiple users simultaneously can also be done in DBMS as the same database will be shared among all the users and by different application programs.

Backup and Recovery Facility: DBMS minimizes the pain of creating the backup of data again and again by providing a feature of ‘backup and recovery’ which automatically creates the data backup and restores the data whenever required.

Enforcement of Integrity Constraints: Integrity Constraints are very important to be enforced on the data so that the refined data after putting some constraints are stored in the database and this is followed by DBMS.

Independence of data: It simply means that you can change the structure of the data without affecting the structure of any of the application programs.

4) What is the purpose of normalization in DBMS?

Answer: Normalization is the process of analyzing the relational schemas which are based on their respective functional dependencies and the primary keys in order to fulfil certain properties.

The properties include:

To minimize the redundancy of the data.
To minimize the Insert, Delete and Update Anomalies.

5) What are the different types of languages that are available in the DBMS?

Answer: Basically, there are 3 types of languages in the DBMS as mentioned below:

DDL: DDL is Data Definition Language which is used to define the database and schema structure by using some set of SQL Queries like CREATE, ALTER, TRUNCATE, DROP and RENAME.

DCL: DCL is Data Control Language which is used to control the access of the users inside the database by using some set of SQL Queries like GRANT and REVOKE.

DML: DML is Data Manipulation Language which is used to do some manipulations in the database like Insertion, Deletion, etc. by using some set of SQL Queries like SELECT, INSERT, DELETE and UPDATE.

6) What is the purpose of SQL?

Answer: SQL stands for Structured Query Language whose main purpose is to interact with the relational databases in the form of inserting and updating/modifying the data in the database.

7) Explain the concepts of a Primary key and Foreign Key.

Answer: Primary Key is used to uniquely identify the records in a database table while Foreign Key is mainly used to link two or more tables together, as this is a particular field(s) in one of the database tables which are the primary key of some other table.

Example: There are 2 tables – Employee and Department. Both have one common field/column as ‘ID’ where ID is the primary key of the Employee table while this is the foreign key for the Department table.

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8) What are the main differences between Primary key and Unique Key?

Answer: Given below are few differences:

The main difference between the Primary key and Unique key is that the Primary key can never have a null value while the unique key may consist of null value.

In each table, there can be only one primary key while there can be more than one unique key in a table.

9) What is the concept of sub-query in terms of SQL?

Answer: Sub-query is basically the query which is included inside some other query and can also be called as an inner query which is found inside the outer query.

10) What is the use of DROP command and what are the differences between DROP, TRUNCATE and DELETE commands?

Answer: DROP command is a DDL command which is used to drop/delete the existing table, database, index or view from the database.

The major difference between DROP, TRUNCATE and DELETE commands are:

DROP and TRUNCATE commands are the DDL commands which are used to delete tables from the database and once the table gets deleted, all the privileges and indexes that are related to the table also get deleted. These 2 operations cannot be rolled back and so should be used only when necessary.

DELETE command, on the other hand, is a DML Command which is also used to delete rows from the table and this can be rolled back.

Note: It is recommended to use the ‘WHERE’ clause along with the DELETE command else the complete table will get deleted from the database.

11) What is the main difference between UNION and UNION ALL?

Answer: UNION and UNION ALL are used to join the data from 2 or more tables but UNION removes duplicate rows and picks the rows which are distinct after combining the data from the tables whereas UNION ALL does not remove the duplicate rows, it just picks all the data from the tables.

12) Explain the concept of ACID properties in DBMS?

Answer: ACID properties is the combination of Atomicity, Consistency, Isolation, and Durability properties. These properties are very helpful in allowing a safe and secure way of sharing the data among multiple users.

Atomicity: This is based on the concept of “either all or nothing” which basically means that if any update occurs inside the database then that update should either be available to all the others beyond user and application program or it should not be available to anyone beyond the user and application program.

Consistency: This ensures that the consistency is maintained in the database before or after any transaction that takes place inside the database.

Isolation: As the name itself suggests, this property states that each transaction that occurs is in isolation with others i.e. a transaction which has started but not yet completed should be in isolation with others so that the other transaction does not get impacted with this transaction.

Durability: This property states that the data should always be in a durable state i.e. any data which is in the committed state should be available in the same state even if any failure or restart occurs in the system.

13) What is Correlated Subquery in DBMS?

Answer: A Subquery is also known as a nested query i.e. a query written inside some query. When a Subquery is executed for each of the rows of the outer query then it is termed as a Correlated Subquery.

Example of Non-Correlated Subquery is:

SELECT * from EMP WHERE ‘RIYA’ IN (SELECT Name from DEPT WHERE EMP.EMPID=DEPT.EMPID);

Here, the inner query is not executed for each of the rows of the outer query.

14) Explain Entity, Entity Type, and Entity Set in DBMS?

Answer:

Entity is an object, place or thing which has its independent existence in the real world and about which data can be stored in a database. For Example, any person, book, etc.

Entity Type is a collection of entities that have the same attributes. For Example, the STUDENT table contains rows in which each row is an entity holding the attributes like name, age, and id of the students; hence STUDENT is an Entity Type which holds the entities having the same attributes.

Entity Set is a collection of entities of the same type. For Example, A collection of the employees of a firm.

15) What are the different levels of abstraction in the DBMS?

Answer: There are 3 levels of data abstraction in the DBMS.

They include:

Physical Level: This is the lowest level of the data abstraction which states how the data is stored in the database.

Conceptual or Logical Level: This is the next level of the data abstraction which states the type of the data and the relationship among the data that is stored in the database.

View Level: This is the highest level in the data abstraction which shows/states only a part of the database.

16) What integrity rules exist in the DBMS?

Answer: There are 2 major integrity rules that exist in the DBMS.

They are:

Entity Integrity: This states a very important rule that value of a Primary key can never have a NULL value.

Referential Integrity: This rule is related to the Foreign key which states that either the value of a Foreign key is a NULL value or it should be the primary key of any other relation.

17) What is E-R model in the DBMS?

Answer: E-R model is known as an Entity-Relationship model in the DBMS which is based on the concept of the Entities and the relationship that exists among these entities.

18) What is a functional dependency in the DBMS?

Answer: This is basically a constraint which is useful in describing the relationship among the different attributes in a relation.

Example: If there is some relation ‘R1’ which has 2 attributes as Y and Z then the functional dependency among these 2 attributes can be shown as Y->Z which states that Z is functionally dependent on Y.

19) What is 1NF in the DBMS?

Answer: 1NF is known as the First Normal Form.

This is the easiest form of the normalization process which states that the domain of an attribute should have only atomic values. The objective of this is to remove the duplicate columns that are present in the table.

20) What is 2NF in the DBMS?

Answer: 2NF is the Second Normal Form.

Any table is said to have in the 2NF if it satisfies the following 2 conditions:

A table is in the 1NF.

Each non-prime attribute of a table is said to be functionally dependent in totality on the primary key.

DBMS Interview Theory Questions

Q1. What are super, primary, candidate and foreign keys?

Ans: A super key is a set of attributes of a relation schema upon which all attributes of the schema are functionally dependent. No two rows can have the same value of super key attributes.
A Candidate key is minimal superkey, i.e., no proper subset of Candidate key attributes can be a superkey.
A Primary Key is one of the candidate keys. One of the candidate keys is selected as most important and becomes the primary key. There cannot be more that one primary keys in a table.
Foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table.

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Q2. What are the differences between DDL, DML and DCL in SQL?

Ans: Following are some details of three.
DDL stands for Data Definition Language. SQL queries like CREATE, ALTER, DROP and RENAME come under this.
DML stands for Data Manipulation Language. SQL queries like SELECT, INSERT and UPDATE come under this.
DCL stands for Data Control Language. SQL queries like GRANT and REVOKE come under this.

Q3. What is a Trigger?

Ans: A Trigger is a code that associated with insert, update or delete operations. The code is executed automatically whenever the associated query is executed on a table. Triggers can be useful to maintain integrity in database.

Q4. What is a stored procedure?

Ans: A stored procedure is like a function that contains a set of operations compiled together. It contains a set of operations that are commonly used in an application to do some common database tasks.

Q5. Explain the concept of ACID properties in DBMS?

Atomicity: This is based on the concept of “either all or nothing” which basically means that if any update occurs inside the database then that update should either be available to all the others beyond user and application program or it should not be available to anyone beyond the user and application program.
Consistency: This ensures that the consistency is maintained in the databasebefore or after any transaction that takes place inside the database.
Isolation: As the name itself suggests, this property states that each transaction that is occurring is in isolation with otherse. a transaction which has started but not yet completed should be in isolation with others so that the other transaction does not get impacted with this transaction.
Durability: This property states that the data should always be in a durable statee. any data which is in the committed state should be available in the same state even if any failure or restart occurs in the system.

DBMS Technical Interview Questions:

Q1. Differentiate Nested Loop, Hash Join and Merge Join.

Nested loop (loop over loop)

An outer loop within an inner loop is formed consisting of fewer entries and then for individual entry, inner loop is individually processed.

E.g.

Select col1.*, col2.* from coll, col2 where coll.col1=col2.col2;

It’s processing takes place in this way:

For i in (select * from col1) loop
For j in (select * from col2 where col2=i.col1) loop
Results are displayed;
End of the loop;
End of the loop;

The Steps of nested loop are:

Identify outer (driving) table
Assign inner (driven) table to outer table.
For every row of outer table, access the rows of inner table.

Nested Loops is executed from the inner to the outer as:

outer_loop
inner_loop
Hash join

While joining large tables, the use of Hash Join is preferred.

Algorithm of Hash Join is divided into:

Build: It is a hash table having in-memory which is present on the smaller table.
Probe: this hash value of the hash table is applicable for each second row element.
Sort merge join

Two independent sources of data are joined in sort merge join. They performance is better as compared to nested loop when the data volume is big enough but it is not good as hash joins generally.The full operation can be divided into parts of two:

Sort join operation:

Get first row R1 from input1

Get first row R2 from input2.

Merge join operation:

‘while’ is not present at either loop’s end.
if R1 joins with R2
next row is got R2 from the input 2
return (R1, R2)
else if R1 < style=””> next row is got from R1 from input 1
else
next row is got from R2 from input 2
end of the loop

Q2. How to create Table?

Ans: For creating a Table in database, we have to use ‘CREATE TABLE’ Statement.

For Example:

CREATE TABLE “SomeName”

(“col1” “datatype”,

(“col2” “datatype”);

Q3. What is a Join?

Ans: An SQL Join is used to combine data from two or more tables, based on a common field between them. For example, consider the following two tables.

Student Table

ENROLLNO	STUDENTNAME	ADDRESS
1000	geek1	geeksquiz1
1001	geek2	geeksquiz2
1002	geek3	geeksquiz3

Student Course Table

COURSEID	ENROLLNO
1	1000
2	1000
3	1000
1	1002
2	1003

Following is join query that shows names of students enrolled in different courseIDs.

SELECT StudentCourse.CourseID, Student.StudentName

FROM StudentCourse

INNER JOIN Customers

ON StudentCourse.EnrollNo = Student.EnrollNo

ORDER BY StudentCourse.CourseID;

The above query would produce following result.

COURSEID	STUDENTNAME
1	geek1
1	geek2
2	geek1
2	geek3
3	geek1

Q4. What is a view in SQL? How to create one

Ans: A view is a virtual table based on the result-set of an SQL statement. We can create using create view syntax.

CREATE VIEW view_name AS

SELECT column_name(s)

FROM table_name

WHERE condition

Q5. There is a table where only one row is fully repeated. Write a Query to find the repeated row

Name	Section
abc	CS1
bcd	CS2
abc	CS1

In the above table, we can find duplicate row using below query.

SELECT name, section FROM tbl

GROUP BY name, section

HAVING COUNT(*) > 1

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DBMS Interview Questions for Freshers

Database Management System is one of the essentials part of IT Section. Knowledge of DBMS Basics is essential to perform well in the interviews of any IT sector firm including TCS. But answering the DBMS Interview Questions is not an easy task.

There are various vacancies related to DBMS like the SQL Analyst, Database Administrator etc. Some of the top DBMS Interview Questions in TCS provided here will help you in preparing for these interviews in an effective manner.

There are various types of questions that may be asked in the interview like the DBMS SQL Questions or DBMS Technical Questions, RDBMS Interview questions etc.

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Along with these DBMS Viva Questions, you can also download Database Interview Questions and Answers PDF by pressing the direct links facilitated at the top of this page. It is advised to learn more and more DBMS questions and answers in order to develop your knowledge over this section.

Note:

We hope that these DBMS Interview Questions and Answers will help you to great extent in the preparation for related jobs. We will keep on updating these DBMS Interview Questions for Freshers time to time. Therefore, it is advised to bookmark this page by pressing CTRL +D and keep visiting regularly to check further updates of DBMS Interview Questions.

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