Top DBMS Interview Questions In 2023

Data is everywhere these days an astonishing 2.5 quintillion bytes of data are generated in the market daily. All of us must analyze and process this massive amount of data using database management systems (DBMS). Understanding DBMS empowers you to work with data and opens up opportunities to become a Database Administrator. If you’ve read this article on DBMS Interview Questions, you’re already familiar with these facts.

In this article, I’ll be addressing the top DBMS-related questions that frequently come up in interviews. These questions are categorized into generic, SQL-based, and query-based sections, carefully curated from the insights of experts with exceptional skills in this field. So, let’s dive in and explore these questions together.

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Also read: Fundamentals of Database Systems: DBMS Tutorial With PW Skills

DBMS Interview Questions

Q1. What is a Database?

Ans. A Database is like a well-organized and reliable digital storage system for information. It’s designed to be easily updated, accessed, and managed. In a Database, you’ll find collections of tables or objects (anything created using the create command is considered a database object) that hold records and fields.

A row or tuple represents a single entry in a table. In contrast, the basic data storage units containing information about specific aspects of the table are called columns or attributes. When you need to get data from a database, you can use queries to instruct the Database Management System (DBMS) to retrieve the relevant information.

Q2. What makes DBMS a better choice over traditional file-based systems?

Ans. Traditional file-based systems have some shortcomings that make DBMS a much better option. One major issue is the absence of indexing, which means you have to scan the entire page to find the data you need. This makes accessing content slow and tedious. These file-based systems suffer from redundancy and inconsistency. Duplicate and redundant data in files can lead to inconsistencies when one piece of data changes, affecting all the duplicates. Another challenge with traditional file-based systems is the lack of proper concurrency control.

In such systems, if one operation is accessing a file, it may lock the entire page, hindering other operations from working on the same file simultaneously. In contrast, DBMS allows multiple operations to work on the same file concurrently, which is more efficient.

DBMS also addresses various issues that traditional file-based systems struggle with, such as integrity checks, data isolation, atomicity (ensuring that all parts of a transaction are completed or none), and security. These are some reasons why DBMSs have become the preferred choice for managing data efficiently and reliably.

Q3. What are the advantages of the DBMS?

Ans. Here are some of the advantages of using a DBMS (Database Management System):

Data Sharing: With a DBMS, multiple users can simultaneously access and share data from a single database. This enables quick reactions to changes in the database environment, making collaboration and real-time updates much easier.

Integrity Constraints: A DBMS allows data to be stored, organized, and refined by enforcing integrity constraints. These constraints ensure that the data remains accurate, consistent, and valid, maintaining the overall quality of the database.

Controlling Redundancy: DBMS eliminates redundancy in a database by integrating all the data into a single database. Redundancy, which refers to the repetition of data, is minimized or removed altogether, leading to a more efficient and streamlined data storage system.

Data Independence: One of the great benefits of a DBMS is data independence. This means you can change the data structure without affecting the functioning of the applications that use it. So, you can modify the database layout or schema without having to rewrite the entire application code.

Backup and Recovery: DBMS provides a valuable automatic data backup and recovery feature. Regularly scheduled backups ensure that data is safely stored in case of system failures or data loss incidents. This way, you can easily restore the database to its previous state if needed.

Data Security: Security is a critical aspect of a DBMS. It offers tools and features to enhance data storage and transfer reliability and safety. Authentication only ensures restricted access to authorized users. At the same time, encryption protects sensitive data like one-time passwords (OTP), credit card information, and other confidential details from unauthorized access.

Q4. What are the different languages present in DBMS?

Ans. In a DBMS (Database Management System), there are different languages used for various purposes:

Data Definition Language (DDL): This language consists of commands used to define the structure of the database. It’s all about creating and managing the database itself. Some examples of DDL commands are CREATE (to create new database objects), ALTER (to modify existing objects), DROP (to remove objects), TRUNCATE (to delete data from a table), and RENAME (to rename objects).

Data Manipulation Language (DML): This language includes commands that help manipulate the data stored in the database. In other words, DML deals with the operations performed on the data. Common DML commands are SELECT (to retrieve data), UPDATE (to modify data), INSERT (to add new data), and DELETE (to remove data).

Data Control Language (DCL): DCL commands are used to manage user permissions and control access to the database system. These commands regulate who can perform specific operations on the database. The main DCL commands are GRANT (to give certain permissions to users) and REVOKE (to take back permissions).

Transaction Control Language (TCL): TCL deals with commands controlling database transactions. A transaction is a sequence of one or more database operations executed as a single unit. TCL commands ensure the integrity and consistency of data in the database. The key TCL commands are COMMIT (to save changes made during a transaction), ROLLBACK (to undo changes made during a transaction), and SAVEPOINT (to mark a specific point within a transaction).

Also read: Database Design – Overview, Importance, and Techniques

Q5. What are ACID properties in DBMS?

Ans. ACID properties in DBMS are essential for maintaining a safe and reliable way of sharing data among multiple users. ACID stands for Atomicity, Consistency, Isolation, and Durability. Let’s understand what each of these properties means:

Atomicity: Think of atomicity as an all-or-nothing concept. When a change or update is made to the database, it must either be completed entirely or should not happen. There’s no in-between state. This ensures that a transaction is treated as a single unit. If anything goes wrong during the process, the database will roll back to its initial state, avoiding partial updates that could lead to inconsistencies.

Consistency: This property ensures that the data remains consistent throughout the transaction process. Before and after a transaction, the data should adhere to the defined rules and constraints, maintaining the overall integrity of the database. Any changes made during the transaction should follow the prescribed guidelines to ensure accurate and valid data.

Isolation: Isolation guarantees that each transaction is independent of others. When multiple transactions run concurrently, they should not interfere with each other’s operations. Each transaction should work as if it’s the only one running, and the changes made by one transaction should not be visible to other transactions until it’s completed and committed.

Durability: Durability ensures that once a transaction is successfully completed and committed, its changes become permanent and are not lost, even during system failures or restarts. The data should be durable, meaning it remains intact and in the same state before any unexpected disruptions.

Q6. Explanation of Intension and Extension in a Database:

Ans. The difference between intention and extension in a database lies in their roles and characteristics. Intension, also known as the database schema, is responsible for defining the structure and description of the database during its design phase. It remains unchanged over time and serves as a blueprint for how the data should be organized and stored.

On the other hand, extension refers to the data in the database at a specific time. It represents the current state of the database and changes whenever new data is added (inserted), existing data is updated, or removed (deleted) from the database. An extension can be considered a snapshot of the database at any given moment, and its content dynamically evolves as data operations occur.

Q7. What is the difference between DELETE and TRUNCATE Command in a DBMS?

Ans. In a database management system (DBMS), the DELETE and TRUNCATE commands are used for data manipulation and removal, but they function differently:

DELETE Command:

The DELETE command removes specific rows from a table based on the conditions specified in the WHERE clause.

It targets and deletes only the rows that satisfy the conditions given in the WHERE clause.
This command can be rolled back (undone) if required, allowing for data recovery in case of mistakes.
The DELETE command logs each row deletion, which can make the process slower, especially for large datasets.

TRUNCATE Command:

The TRUNCATE command removes all data from a table, effectively resetting it to its initial state.

Unlike DELETE, there is no WHERE clause in TRUNCATE, making it remove all rows in one go.
TRUNCATE cannot be rolled back, meaning the deleted data is not recoverable after execution.
TRUNCATE does not log individual row deletions so it can be significantly faster than DELETE, especially for large tables.

Q8. Explain the shared lock and exclusive lock in a Database Transaction

Ans. Locks in a database protect shared pieces of data from being simultaneously updated or modified by multiple users. The main difference between shared locks and exclusive locks is their purpose and behavior during transactions:

Shared Lock:

A shared lock is acquired when a transaction needs to read a data item.
Multiple transactions can hold a shared lock on the same data item simultaneously.
The shared lock allows multiple transactions to read the data item concurrently, ensuring data consistency during reading operations.

Exclusive Lock:

An exclusive lock is required when a transaction is about to perform a write operation (insert, update, or delete) on a data item.
Only one transaction can hold an exclusive lock on a data item at anytime.
Exclusive locks prevent multiple transactions from modifying the same data simultaneously, ensuring data integrity and avoiding conflicts.

Q9. Explanation of Normalization and Denormalization

Ans. Normalization and denormalization are two opposing processes used in database design:

Normalization:

Normalization is a method of organizing data to reduce redundancy and improve data integrity.
It involves breaking down data into multiple tables and ensuring each table serves a single purpose, adhering to specific rules (normal forms).
Normalization helps optimize disk space usage and prevents inconsistencies by reducing duplicate data.

Denormalization:

Denormalization is the reverse process of normalization, where tables that have been broken down are combined into a single table.
Denormalization aims to enhance data retrieval performance, especially for complex queries, by reducing the need for JOIN operations.
While denormalization can improve query speed, it may lead to some data redundancy and requires careful consideration to maintain data integrity.

Q10. What do you mean by query optimization?

Ans. Query optimization refers to the process of finding the most efficient way to evaluate a database query. When you run a query on a database, there could be multiple ways to achieve the same result, but query optimization aims to identify the approach that takes the least time and resources.

Also read: What Is a Database? Definition, Types, Uses, Advantages

FAQs

How important is DBMS for job placement?

DBMS is necessary for job placement as it's a crucial subject in computer science courses, included in placement exams, and a prerequisite for learning in most Data Science companies.

How can I prepare for DBMS?

To prepare for DBMS, start with the basics. Understand concepts like functional dependency, attribute closure, equivalence of functional dependencies, and canonical cover.

What is SQL?

SQL is an abbreviation for Structured Query Language. It is a programming language used for manipulating and accessing relational databases.

Can I learn DSA within 6 months?

Learning DSA requires a substantial investment of time and effort. It may take 4 to 8 months to master it truly. You must dedicate enough time and effort to it.

What are the benefits of using a DBMS over Excel?

DBMS allows real-time collaboration and easy linking between tables, unlike Excel.