DBMS Interview Q & A

Top 30 DBMS interview questions and answers

1.What is DBMS ?

DBMS stands for “Database Management System”.

DBMS is collection of program/application system which enables the user to create and maintain the database.

It provides an interface in which user can perform different operations such as creating database,inserting data into the database,deleting data from the database,updating data into the database etc.

It is used to store data in secure manner.

2. What is Database ?

In simple manner,Database is collection of data in a consistent and well -organised manner.

It facilitate the user to easily access and manage the data.

3.What do you mean Database System ?

When we combine the DBMS and Database then it is known as Database System.

4.What are the advantage of DBMS as compare to traditional file-based system ?

  • Redundancy is controlled
  • Data sharing
  • providing the backup and recovery
  • providing the multiple user interfaces
  • maintain data consistent
  • Secure

5 What is RDBMS ?

RDBMS stands for “Relational Database Management System”.

It is used to store and maintain the data in form of “rows and columns” or table.

It facilitate the user to perform different operation such as insert,update,delete,modify etc.

6 What is SQL ?

SQL stands for “Structured Query Language”.

It is used to interact with the “RDBMS” for accessing and manipulating the data.

7 What is normalization ?

Normalization is the process which is used to remove the redundant data from the database

It also remove the duplicate data from the database.

8 What is advantage of normalization ?

There are the different advantage of normalization:

  • Remove the duplicate entry
  • It minimize the data redundancy
  • It saves time and storage
  • It reduce the insert,delete and update anomalies

9 What are the languages supported by DBMS ?

There are the four types of language supported by the DBMS.

  • DDL stands for “Data Definition Language”.SQL queries are CREATE,ALTER,DROP,TRUNCATE &RENAME.
  • DML stands for “Data Manipulation Language”.SQL queries are SELECT,INSERT,UPDATE & DELETE.
  • DCL stands for “Data Control Language”.SQL queries are GRANT and REVOKE
  • TCL stands for “Transnational Control language.SQL queries are COMMIT & ROLLBACK.

10 What is the difference between the primary key and unique key ?

Primary key can never contain null value while unique key may contain null value.

There can be only one primary key in a table while unique key may be one or more.

11 What is Data Model ?

Data model is a concept which describe that how data can be stored,organised and manipulated into the database.

Some data models are:

  • Network data model
  • E-R model
  • relation model
  • so on

12 What are the disadvantage of file-processing system ?

  • Security problem
  • Limited data sharing problem
  • Integrity problem
  • Inconsistency of data problem
  • Data isolation problem

13 What do you mean by data abstraction ?

Data abstraction is the process of hiding the implementation of database from the user only showing the functionality of the database.

14 What is the difference between the DELETE and TRUNCATE ?

‘DELETE’ is used to remove the rows from the table by using where condition.It can be COMMIT and ROLLBACK.

‘TRUNCATE’ is used to remove all the rows from the tables.It can not be COMMIT and ROLLBACK.

15 Explain different levels of data abstraction in DBMS.

There are the three levels of data abstraction in DBMS.

  • Physical Level:This is the lowest level of data abstraction which tells that how data is stored in database.
  • Logical Level:This is the middle level of data abstraction which tells that what data is stored in database.
  • View Level:This is upper level of data abstraction which only show the part of database.

16 Explain data integrity rule in DBMS.

Data integrity rules ensure that data stored in the database is a secure and consistent.

There are two types of data integrity rule in DBMS

  • Entity integrity:It ensure that primary key cannot have NULL value or primary key cannot be NULL.
  • Referential integrity:It ensure that foreign key may be NULL or should be the primary key for the other tables/relation.

17 What is Constraint in DBMS ?

It is used to set the condition on the data types of tables.It can do during the creating and altering the table.

Some Constraint are given below:

  • PRIMARY KEY
  • NOT NULL
  • UNIQUE
  • FOREIGN KEY
  • CHECK

18 What do you mean by E-R model in DBMS ?

E-R model means Entity-Relationship model.It is based on the concept of entities and relationship between them.

19 What do you mean by weak and strong entity set ?

When the entity set does not have attribute to make primary key then it is known as weak entity set.It does not contain primary key.

When the entity set have attribute to make primary key then it is known as strong entity set.It contains primary key.

20 What do you mean by entity set ?

The collection of entries in the database of any particular of entry is known as entity set.

Example: set of books,set of computer,set of school etc.

21 What do you mean entity ?

An entity may be any type of objects/things which independently exist in the world.

Example:pen ,pencil,books and chair etc

22 What do you mean by ACID property ?

The ACID property ensure that every transactions are secure and integrity.

  • Atomicity:It ensure that every transactions has atomic or single unit which means transaction is succeeds or failed.
  • Consistency: It ensure that the flow of data is consistent that is database is consistent before or after the transactions.
  • Isolation:It ensure that the transactions are executed concurrently without disturbing the database.
  • Durability:It ensure that once a transaction is committed.It will remain committed if the system crash or power off.

23 What do you mean by 2-Tier architecture ?

2-Tier architecture is same as Client-Server architecture.

In 2-Tier architecture the direct communication takes place between the client end and database at the server side.It means there is no intermediate between the client and server.

24 What do you mean by 3-Tier architecture ?

In the 3-Tier architecture one intermediate exist between the client and server.that means GUI(graphical user interface).

In the 3-Tier architecture,client/user first have to interact with the application GUI(graphical user interface) or application on the server side after that further communicate with the database.

Note:3-Tier is more secure as compare to 2-Tier architecture.

25 What do you mean by join in SQL?

It helps to make relationship between the two tables.

It is used to combine rows from the two or more tables.

#Types of join

  • Inner join
  • Left join
  • Right join
  • Full join

26 What are the types of normalization form ?

There are various normalization form which is given below

  • 1NF(First normal form)
  • 2NF(Second normal form)
  • 3NF(Third normal form)
  • BCNF(Boyce codd normal form)

27 What do you mean by Trigger?

Trigger is a procedure which get executed automatically whenever new action occur in the database.

Example:suppose we want to add student in the “student_list” table then it will automatically added with the specified column of “student_list” table.

28 What do you mean by aggregate function ?

It is used to perform calculation on the “data present in the column” and it return single value.

Example:sum( ), max( ), min( ) and count( ) etc

29 What do you mean by BCNF ?

BCNF stands for “Byoce codd normal form”.

Rules:

  • A table should be in 3NF
  • Each functional dependency x->y that exist.x is the super key of table

30 How we can interact with the RDBMS ?

We can interact with the RDBMS by the help of SQL(structured query language).