Top 30 Database Interview Questions and Answers (2023)

Are you preparing for a job interview in database? Here is most asked Database Interview Questions and answers. It’s important to be well-versed in the most common questions that are asked during database-related interviews. In this post, we are sharing top 30 dbms interview questions and answers that you should know in 2023. From basic to advance interview questions everything you need to know to impress your interviewer and land your dream job. You can also visit our YouTube Channel EasyWay2Learn to see our Online Training videos.

Most asked Database Interview Questions and Answers (2023)

1. What do you understand by term Database?

A database is a collection of organized data which stored and accessed electronically. The data is typically organized into tables, which contain rows (records) and columns (fields). The tables are related to one another through relationships, which allow data to be queried and accessed in a logical and meaningful way.

Database is used to store and manage a wide variety of data, including financial records, customer information, inventory, and many more.

In general, databases are designed to be efficient, secure, and scalable, making them an important tool for storing and managing data in today’s digital world.

2. What do you understand by DBMS?

DBMS stands for database management system. It is a software program that allows users to create, manage, and maintain a database.

With the help of DBMS, user can store, organize and manipulate the data in different ways. It includes a set of tools and functions that enable users to create and manage database structures and perform other operations on the data.

There are several types of DBMSs available, including relational DBMSs (RDBMSs), object-oriented DBMSs (OODBMSs), and NoSQL DBMSs. Each type has its own characteristics and is suited for different types of data and applications.

3. What is RDBMS.

RDBMS stands for relational database management system. It is a database management system (DBMS) that is based on the relational model. Which organizes data into tables (also known as relations) with rows (records) and columns (fields).

In a RDBMS, data is stored in tables and can be related to other tables through the use of keys and indexes. This allows data to be queried and accessed in a logical and meaningful way.

Some examples of RDBMSs include MySQL, Oracle, and Microsoft SQL Server. These systems use Structured Query Language (SQL) to create and manipulate database and perform other operations on the data.

4. Explain the advantages of DBMS.

There are several advantages to using a database management system (DBMS) and few are mentioned below:

Data Organization: DBMS allows data to be organized in a logical and meaningful way. Which make it easier to access and analyze.

Data Security: DBMS provides a number of security features. Such as user authentication and data encryption, to protect from unauthorized access.

Data Integrity: Data Base Management System ensures that data is accurate and consistent. It can automatically detect and correct errors.

Data Independence: DBMS allows users to access and manipulate data without knowing how the data is stored or structured. This makes easier to change the underlying database design without affecting the applications that use the data.

Data Manipulation: A DBMS provides a range of tools and functions for accessing, updating, and querying data, making it easier to manage and analyze large volumes of data.

Data Sharing: It allows multiple users to access and manipulate the same data simultaneously. Making it easier to share and collaborate on data within an organization.

Data Backup and Recovery: It provides features for backing up and recovering data. Which is important for preserving data in case of system failures or other disasters.

Overall, a DBMS can help organizations to efficiently and effectively store, retrieve, and analyze data, making it an important tool for many types of applications.

5. Explain What is Data Redundancy?

Data redundancy refers to the duplication of data within a database. It occurs when the same data is stored in multiple places within a database or in multiple databases.

Data redundancy can be a problem because it can lead to inconsistencies and errors in the data. For example, if the same data is stored in multiple places and one of those copies is updated. Then other copies may not be updated to reflect the changes. This can result in conflicting or outdated data.

Data redundancy can also lead to inefficiencies in the database, as it can take up unnecessary space and make it more difficult to manage and maintain the data.

6. Explain, what are the different types of relationships in Database?

In a database, relationships are used to connect and associate data from different tables. There are three main types of relationships that can exist between tables in a database:

One-to-one relationships: A one-to-one relationship exists between two tables when each record in the first table is related to exactly one record in the second table, and vice versa. For example, a table of employees may have a one-to-one relationship with a table of employee contact information, with each employee having a unique set of contact details.

One-to-many relationships: A one-to-many relationship exists between two tables when a record in the first table can be related to multiple records in the second table, but each record in the second table is related to only one record in the first table. For example, a table of customers may have a one-to-many relationship with a table of orders, with each customer being able to place multiple orders, but each order being associated with only one customer.

Many-to-many relationships: A many-to-many relationship exists between two tables when a record in the first table can be related to multiple records in the second table, and vice versa. For example, a table of courses may have a many-to-many relationship with a table of students, with each course being taken by multiple students and each student taking multiple courses.

7. What Normalization and De-Normalization.

Normalization is the process of organizing a database in a way that reduces redundancy and dependency. It is a design technique that is used to eliminate data redundancy and improve the efficiency of a database.

The goal of normalization is to divide a database into smaller, more specialized tables that are more closely related to one another. This helps to reduce data redundancy and improve the integrity of the data.

De-normalization is the opposite of normalization. It is the process of adding redundancy to a database in order to improve performance. De-normalization is often used in cases where the performance of a database is more important than the integrity of the data.

De-normalization can involve adding redundant copies of data to tables, renormalizing tables by combining them. Or using other techniques to add redundancy to the database. However, it is important to carefully consider the trade-offs between performance and data integrity when deciding whether or not to de-normalize a database.

8. What are the different types of Normalization?

First normal form (1NF): A database is in first normal form if all of its tables have a primary key and all of the data in each table is atomic (meaning that it cannot be divided into smaller pieces).

Second normal form (2NF): A database is in second normal form if it is in 1NF and all of its tables are in second normal form. To be in second normal form, a table must meet the following criteria: It must be in 1NF, and all of its non-primary key columns must be dependent on the primary key.

Third normal form (3NF): A database is in third normal form if it is in 2NF and all of its tables are in third normal form. To be in third normal form, a table must meet the following criteria: it must be in 2NF, and all of its columns must be directly dependent on the primary key.

Boyce-Codd normal form (BCNF): A database is in Boyce-Codd normal form (also known as third normal form) if it is in 3NF and all of its tables are in BCNF. To be in BCNF, a table must meet the following criteria: it must be in 3NF, and all of its functional dependencies (columns that depend on other columns) must be on the primary key.

Fourth normal form (4NF): A database is in fourth normal form if it is in BCNF and all of its tables are in 4NF. To be in 4NF, a table must meet the following criteria: it must be in BCNF, and it must not have any multi-valued dependencies (columns that depend on more than one column).

Fifth normal form (5NF): A database is in fifth normal form if it is in 4NF and all of its tables are in 5NF. To be in 5NF, a table must meet the following criteria: it must be in 4NF, and it must not have any join dependencies (columns that depend on other tables).

Normalization is an important process for ensuring the efficiency and integrity of a database. It helps to eliminate data redundancy, improve the performance of database queries, and ensure that data is stored in a logical and consistent way.

9. What is Boyce-Codd normal form (BCNF)?

Boyce-Codd normal form (BCNF) is a normal form in database normalization. It is a stronger version of the third normal form (3NF) and is used to prevent certain types of data anomalies that can occur in a database. In order to be in BCNF, a relational database table must meet two criteria:

1. It must be in 3NF.
2. All determinants in the table must be a candidate key.

A determinant is a column or set of columns that uniquely identifies a row in the table. A candidate key is a set of columns that can be used as a primary key for the table, but may not necessarily be the primary key.

BCNF helps to ensure that the data in a database is free from certain types of update, insertion and deletion anomalies. And it is used to design databases that are less prone to data inconsistencies.

SQL Interview Questions and Answers

10. What is SQL?

SQL (Structured Query Language) is a programming language used for managing and manipulating relational databases. It is used to insert, update, and query data in a database. SQL is the standard language for relational database management systems, such as MySQL, Oracle, and Microsoft SQL Server.

11. How many SQL statements are used? Explain them.

There are several types of SQL statements that can be used to manipulate and manage data in a database. Here is a list of the most common types of SQL statements:

Data Definition Language (DDL) statements: DDL statements are used to create and modify the structure of a database. Such as creating or altering tables, indexes, and views. Examples of DDL statements include CREATE, ALTER, and DROP.

Data Manipulation Language (DML) statements: DML statements are used to manipulate data in a database. Such as inserting, updating, or deleting records. Examples of DML statements include INSERT, UPDATE, and DELETE.

Data Query Language (DQL) statements: DQL statements are used to retrieve data from a database. Such as selecting specific records or performing calculations on the data. Examples of DQL statements include SELECT and SET.

Data Control Language (DCL) statements: DCL statements are used to control access to a database. Such as granting or revoking permissions for users. Examples of DCL statements include GRANT and REVOKE.

Transaction Control Language (TCL) statements: Thise statements is used to manage transactions in a database. Such as committing or rolling back changes. Examples of TCL statements include COMMIT and ROLLBACK.

Each of these types of SQL statements serves a specific purpose and can be used in different contexts to manage and manipulate data in a database. Together, they provide a powerful toolkit for working with databases and can be used to perform a wide range of tasks.

12. Give some examples of commands DDL, DML, and DCL.

Here are some examples of SQL commands:
Data Definition Language (DDL) statements:
                   CREATE TABLE: Creates a new table in the database
                   ALTER TABLE: Modifies the structure of an existing table
                   DROP TABLE: Deletes a table from the database
Data Manipulation Language (DML) statements:
                  INSERT INTO: Inserts a new record into a table
                  UPDATE: Modifies existing records in a table
                  DELETE FROM: Deletes records from a table
Data Control Language (DCL) statements:
                 GRANT: Grants a specific type of access or privilege to a user or role
                 REVOKE: Revokes a specific type of access or privilege from a user or role
These are just a few examples of the types of SQL commands. That can be used to manipulate and manage data in a database. There are many other commands and clauses that can be used to perform a wide variety of tasks.

13. Explain about DML Compiler.

A DML compiler is a software component that translates Data Manipulation Language (DML) statements into machine-readable code. That can be executed by a database management system (DBMS).

DML is a type of SQL (Structured Query Language) that is used to manipulate data in a database. Such as inserting, updating, or deleting records. A DML compiler is responsible for converting DML statements into code that the DBMS can understand and execute.

The DML compiler is an important component of a DBMS and plays a key role in the execution of DML statements. It is responsible for parsing and analyzing the DML statements. Checking for syntax errors and other issues. Generating the appropriate code to execute the statements.

The DML compiler is typically part of the DBMS software. It is transparent to users, who typically interact with the database using SQL commands.

14. What is DDL interpreter?

A DDL interpreter is a software component that interprets and executes Data Definition Language (DDL) statements in a database management system (DBMS).

DDL is a type of SQL (Structured Query Language). That is used to define the structure and organization of a database. Such as creating or altering tables, indexes, and views.

DDL interpreter is responsible for interpreting DDL statements. And executing the appropriate actions to create or modify the database structure.

The DDL interpreter is typically part of the DBMS software. It is transparent to users, who typically interact with the database using SQL commands.

15. Explain the advantages of using SQL.

There are several advantages of using SQL:

• SQL is easy to learn and use: The syntax of SQL is simple and easy to understand, making it a great choice for beginners.

• SQL is a standard language: SQL is a widely-used, standard language for managing relational databases. This means that it can be used across different platforms and with different types of databases.

• SQL is powerful: SQL has a wide variety of commands and functions that can be used to manipulate and query data in a database.

• SQL is efficient: SQL is designed to work with large amounts of data. It is optimized for performance, making it a fast and efficient language for working with databases.

• SQL is widely supported: SQL is supported by most relational database management systems. It also supported by many programming languages, such as Python, Java, and C#.

• SQL is widely used in industry and business, that makes it easy to find support, tutorials and solutions online, and finding a job with SQL skills is easy.

16. Explain what is ‘Record’, ‘Field’ and ‘Table’ in terms of database?

In a database, a record is a collection of related information about a specific entity. For example, in a database of employee records, each record would represent the information about a single employee. Such as their name, job title, salary, and contact information.

A field is a specific piece of information within a record. Continuing with the example of an employee database, fields might include the employee’s first name, last name, email address, and phone number.

A table in a database is a structured collection of data that is organized into rows and columns. Each row in a table represents a single record, and each column represents a specific field or attribute of that record.

17. What do you understand by Data Independence? What are the types?

Data independence refers to the ability to change the schema (structure) of the database without affecting the application programs that access the data. There are two types of data independence:

Logical data independence: This refers to the ability to change the logical organization of data in the database. Such as adding, modifying or removing tables, fields or relationships without affecting the application programs that access the data.

Physical data independence: This refers to the ability to change the physical storage of data in the database. Such as changing the storage device or file organization without affecting the application programs that access the data.

18. Explain the relationship between ‘View’ and ‘Data Independence’.

In a database, a view is a virtual table that is based on a SELECT statement. A view does not store data itself, but rather displays data from the underlying tables or views that it is based on.

Views can be used to provide data independence in a database by allowing users to access data in a specific way. For example, a view might be created to display only certain fields from a table. Or to filter or sort the data in a specific way. This allows users to access the data in a way that is meaningful to them.

Views can also be used to provide security and data integrity in a database by allowing users to access only the data that they are authorized for. For example, a view might be created to show only certain fields or records to certain users, while hiding sensitive information from unauthorized users.

Overall, views can be an important tool for providing data independence and security in a database. As it allows users to access and manipulate data in a way that is meaningful to them without knowing the details of how the data is stored in database.

19. What are the advantages and disadvantages of views in the database?

Views are virtual tables in a database that are created based on a SELECT statement. They allow users to store a SELECT statement in the database. And treat it like a table, without actually storing the data in the table.

Some advantages of views in a database include:

Simplicity: Views can simplify the complexity of a database by abstracting away the details of the underlying tables. It only shows the relevant data to the user.
Security: Views can be used to restrict access to certain data by only showing a subset of the columns or rows in a table.

Performance: Views can improve the performance of certain queries by pre-calculating. It store the results of the SELECT statement, which can reduce the amount of time required to execute the query.

Maintainability: Views can help to improve the maintainability of a database by centralizing common queries in a single location. And making it easier to modify the underlying data structures without affecting the users of the database.

Some disadvantages of views in a database include:

Limited functionality: Views are read-only and cannot be used to insert, update, or delete data from the underlying tables.
Dependency: If the underlying tables that a view depends on are modified or deleted, the view may become invalid or produce incorrect results.

Performance: If a view relies on a complex SELECT statement or involves multiple tables. It may have a negative impact on performance when it is used in a query.

Limited flexibility: Views cannot be used in all situations where a regular table can be used. Such as in the FROM clause of a SELECT statement or as the target of an INSERT, UPDATE, or DELETE statement.

20. Explain Functional dependency?

Functional dependency is a concept in database design and relational theory. It describes the relationship between attributes in a relational database.

A functional dependency (FD) exists between two sets of attributes, X and Y. When the value of X uniquely determines the value of Y. This can be represented as X -> Y, where X is the determinant attribute and Y is the dependent attribute.

For example, in a database of students. If we have a table with the attributes (student_id, student_name, student_address, student_phone) and we know that for each student_id. There is a unique student_name,student_address and student_phone, we can say that student_id functionally determines student_name, student_address, and student_phone.

21. What is the difference between a primary key and a foreign key?

A primary key is a field or set of fields in a table that uniquely identifies each record in the table. It is used to ensure data integrity and to create relationships with other tables. A primary key is also used as an index to speed up queries on the table.

A foreign key is a field or set of fields in a table that is used to create a link between the data in two tables. It is used to establish and enforce a link between the data in two tables based on the values of the primary key in the primary table. A foreign key in a table references the primary key of another table. The main purpose of a foreign key is to maintain referential integrity between related tables.

22. What is a stored procedure and why is it used?

A stored procedure is a pre-compiled collection of SQL statements that are stored in the database. Stored procedures are used to perform specific tasks. Such as inserting, updating or retrieving data.

Stored procedures are used for a number of reasons:

Performance: Stored procedures are pre-compiled, which means that the database only needs to parse and optimize them once. This can lead to a significant performance improvement when compared to executing the same SQL statements multiple times.

Security: Stored procedures can be used to implement security controls. Database administrators can grant or revoke access to stored procedures. Rather than giving users access to the underlying tables.

Reusability: Stored procedures can be called from multiple applications or modules. Which leads to reduced development time and increased code reuse.

Centralized Business Logic: Stored procedures can contain complex business logic that can be executed in the database. This eliminates the need to duplicate the logic in different parts of the application.

Abstraction: Stored procedures can abstract the underlying table structures and relationships, making it easier to change the database schema without affecting the application.

Portability: Stored procedures can be used to insulate the application from changes in the underlying database management system.

In summary, Stored procedures are pre-compiled collection of SQL statements that are stored in the database. It used for performance, security, reusability, centralized business logic, abstraction and portability.

23. How do you handle database performance issues?

There are several ways to handle database performance issues:

Indexing: Creating indexes on frequently-searched fields can greatly improve query performance. However, it is important to note that creating too many indexes can negatively impact performance.

Optimizing queries: Reviewing and optimizing the SQL queries that are causing performance issues can help to improve performance. This can include making sure that queries are using indexes and that they are not retrieving more data than is necessary.

Partitioning: Partitioning large tables can improve performance by allowing the database management system to access smaller subsets of data.

Normalization: Normalizing the database can help to improve performance by reducing data redundancy and eliminating data inconsistencies.

Monitor and Analyze: Monitoring the database performance regularly and analyzing the performance metrics. Can help to identify the bottlenecks and areas that need improvement.

Scaling: Scaling the database horizontally or vertically can improve the performance by increasing the resources. Such as system memory, CPU, storage available to the database.

Caching: Caching frequently used data can greatly improve performance by reducing the number of database accesses required.

Upgrading the database management system or hardware can also improve performance if the current system is outdated or underpowered.

It’s important to note that performance tuning is an iterative process and requires monitoring. Testing and adjusting different approaches until the best performance is achieved. It is also important to consider the trade-offs between performance and other factors such as cost, scalability and maintenance.

24. What is the difference between a clustered and a non-clustered index?

A clustered index determines the physical order of data in a table. Each table can have only one clustered index because the data rows themselves can be stored in only one order.

A non-clustered index is a separate object that contains a copy of some or all of the columns in a table along with a pointer to the full row. Each table can have multiple non-clustered indexes.

25. Explain types of Database?

In today’s digital era, data plays a crucial role in various aspects of our lives. From managing customer information to processing large volumes of data, databases are the backbone of modern information systems. In this article, we will delve into the world of databases and explore different types that exist.

Relational Databases: Relational databases are one of the most prevalent types of databases used today. They store data in tables with rows and columns, forming relationships between different tables.

Object-Oriented Databases: Object-oriented databases (OODBs) are designed to store and manage complex data structures, including objects, classes, and inheritance relationships.

Hierarchical Databases: Hierarchical databases organize data in a tree-like structure, with parent-child relationships. They have a top-down approach, where each record has a single parent but can have multiple children.

Network Databases: Network databases expand upon the hierarchical model by allowing many-to-many relationships between records. They connect records through pointers, forming complex data networks.

NoSQL Databases: NoSQL (Not Only SQL) databases are a category of databases that depart from the traditional relational model. They offer flexible schemas and scalable storage, making them suitable for handling large volumes of unstructured data.

26. Explain What is Database Schema?

In the world of databases, a database schema serves as a blueprint or structure that defines the organization, relationships, and constraints of a database system. It acts as a framework that outlines the logical and physical representation of data within the database.

A database schema can be defined as a collection of metadata that describes the structure of a database. It defines the tables, fields, relationships, and constraints that make up the database. The schema provides a formal way to represent the logical and physical organization of data, allowing users to understand and interact with the database efficiently.

27. What is Visual Novel Database?

Visual novels have gained immense popularity in the gaming and storytelling communities. With their unique blend of interactive storytelling and captivating visuals, visual novels offer players an immersive narrative experience. To help enthusiasts and newcomers alike, a Visual Novel Database (VNDB) serves as a valuable resource. In this article, we will explore what a Visual Novel Database is, its purpose, and how it benefits both developers and players.

28. What is the role of database administrator?

In the realm of databases, a Database Administrator (DBA) plays a crucial role in ensuring the efficient and secure management of an organization’s data. DBAs are responsible for various tasks related to the design, implementation, maintenance, and security of databases. In this article. We will delve into the role of a Database Administrator and the significance of their contributions to an organization’s data infrastructure.

Responsibilities of a Database Administrator

• Database Design and Creation: DBAs collaborate with developers and analysts to design and create database systems that meet the organization’s requirements. They determine the optimal database structure, define tables and relationships, and establish data integrity constraints.

• Installation and Configuration: DBAs are responsible for installing and configuring database management systems (DBMS) on servers and ensuring compatibility with the underlying infrastructure. They set up user accounts, security measures, and access controls to protect sensitive data.

• Data Backup and Recovery: DBAs implement robust backup and recovery strategies to safeguard critical data. They schedule regular backups, test restoration procedures, and monitor backup performance to minimize data loss in the event of system failures or disasters.

• Performance Monitoring and Tuning: DBAs continuously monitor database performance, identifying and resolving bottlenecks to optimize system efficiency. They analyze query execution plans, fine-tune database parameters, and implement indexing strategies to improve query response times.

• Security and Access Control: DBAs establish and enforce security measures to protect data from unauthorized access, ensuring compliance with privacy regulations. They manage user permissions, implement encryption techniques, and monitor database activity for any suspicious behavior.

• Database Maintenance and Upgrades: DBAs perform routine maintenance tasks such as database defragmentation, data reorganization, and index rebuilding to optimize storage and performance. They also plan and execute database upgrades, ensuring seamless transitions to new versions or patches.

• Troubleshooting and Issue Resolution: DBAs act as the first line of defense in diagnosing and resolving database-related issues. They analyze error logs, perform root cause analysis, and collaborate with developers and system administrators to resolve performance problems, data inconsistencies, or system failures.

29. How do you backup and restore a database?

In Summary, please keep in mind Database is very vast area and interviewer may ask other questions based on the requirement. You can also see our other Blog Post here.