One such topic that is crucial for getting into IT is Database Management System (DBMS). Typical company questions related to databases are database, SQL, keys, normalisation, transactions, and database design, where they need to check the candidate's basics in data management.
While these questions mainly consist of technical queries, being familiar with the common DBMS interview questions would serve you well in an interview and help you answer them confidently. This guide contains FAQs in parentheses, which will be easier to understand for freshers and even candidates preparing to crack interviews.

What Is a DBMS?

Software that is used to create, maintain, and manage a database — a Database Management System. It allows users to manage data without having to work through all the information manually.
Some well-known examples of database management systems are as follows: MySQL, Oracle Database, Microsoft SQL Server, and PostgreSQL.
You are also trained, for example, to control access to data, maintain the accuracy of your data, and minimise unnecessary duplication.

What Is a Database?

A database is a structured way to store, retrieve, and organise data.
For instance, a college database may have fields such as student names, roll numbers, courses, marks, and contact details. This information is worked with the help of a Database Management System (DBMS).

At least DBMS vs RDBMS (difference)?

DBMS is a generic database management system, whereas RDBMS software implementation is based on the relational model.
As a relational database management system (RDBMS), it primarily stores data in rows and columns of tables. Relationships can also connect tables.
Typical RDBMSs are MySQL, Oracle Database, PostgreSQL, and SQL Server.
The key distinction is that RDBMS revolves around the relationships among tables and usually adheres to relational database rules. Before appearing for a technical interview, candidates should prepare Important DBMS Interview Questions covering databases, SQL, keys, normalization, transactions, and database design.

What Is a Table?

Tab: A table is the simplest structure used to store data in a relational database.
It consists of:

• Rows, which represent individual records

• Columns, which are, by definition, enlarging attributes or fields
  You may have a table with the following columns in the case of Students: Student_ID, Name, Age, and Course. There would be separate rows per student.

What Is a Primary Key?

Primary Key: A column or set of columns that uniquely identifies each record in a table.
For instance, if the key is Student_ID, then every student can have a unique ID, and thus you can treat it as a primary key.
Characteristics of a Primary Key Include:

• It must contain unique values.

• It cannot contain NULL values.

• Only one primary key exists for a table at all times.

• It may contain one or more columns.

What Is a Foreign Key?

The FOREIGN KEY is a column that creates a link between two tables. This is typically a foreign key to the primary key of another table.
Example: in an Employee table, Department_ID must refer to that id_ in the Department table.
Foreign key relationships and dependency between tables.

What Is a Candidate Key?

Candidate keys are a column or group of columns used to uniquely identify a record.
There can be multiple candidate keys for a table, but one of the candidate keys is chosen as the primary key.
One of the best examples can be—if both Student_ID and Email_ID are capable of identifying students uniquely, then both can be candidate keys. Then one can be chosen as a stable key.

What Is Normalisation?

Normalisation is the organisation of a database to eliminate unnecessary duplication and ensure data consistency.
It breaks down large tables into smaller interrelated tables, as well as establishing relationships among those smaller tables.
Common normal forms include:

• First Normal Form (1NF)

• Second Normal Form (2NF)

• Third Normal Form (3NF)

• Boyce-Codd Normal Form (BCNF)
  These DBMS interview questions need to be willing and able to design transaction systems in a computer-oriented interpretation for normalization because it is the most important in designing databases.

What Is Denormalization?

Denormalisation is the deliberate inclusion of some redundant data in a database.
You are based on the data till October 2023 for better training. Normalisation reduces data redundancy, while denormalisation improves query performance at the cost of needing fewer joins.
It is usually adopted when retrieval speed makes it more valuable than avoiding redundancy.

What Is SQL?

Structured Query Language (SQL): Its purpose is to communicate with relational databases.
SQL allows users to do the following:

• Creating tables

• Adding data

• Updating records

• Deleting records

• Retrieving information

• Managing database structures
  For example:

SELECT * FROM Students;

This query fetches records from the Students table.

There are four general categories of SQL commands:

SQL commands are generally categorised into a few categories.
DDL (Data Definition Language): Used to define database structures. These include CREATE, ALTER, DROP, etc.
DML (Data Manipulation Language): It is used to work in data manipulation. Some examples of DML are INSERT, UPDATE, DELETE, and DELETE.
DQL (Data Query Language): Mainly related to read operations using SELECT.
DCL (Data Control Language): Deals with permissions. Examples include GRANT and REVOKE.
TCL (Transaction Control Language): Used to deal with transactions. Examples include COMMIT and ROLLBACK.

What Is a JOIN?

When you need to get records that are related to two or more tables, you use a JOIN.
Common types of joins include:

• INNER JOIN

• LEFT JOIN

• RIGHT JOIN

• FULL OUTER JOIN

• CROSS JOIN
  INNER JOIN, for example, returns records where there is a matching value in both tables.
  Joins are specifically valuable for database and software developers and/or data analysts.

What Is an Index?

An index is a database structure to help the system find records with speed.
It can help speed up some queries, particularly when searching or sorting through large data sets.
On the other hand, indexes take up storage space and might introduce overhead when records are inserted, updated, or deleted. Hence, you should make thoughtful use of indexes.

What Is a Transaction?

A transaction represents a series of database operations that are executed as a single logical unit of work.
For instance, if you want to transfer money between two bank accounts, a function might subtract money from one account and add it to the other. They both need to be treated as a single transaction where both of these operations can be performed properly.
ACID Properties: Transactions are usually described in terms of the ACID properties associated with transactions.

What Are ACID Properties?

ACID stands for Atomicity, Consistency, Isolation, and Durability.

• Atomicity: A transaction is either fully completed or not at all

• Atomic: A transaction must move the database from one valid state to another valid state.

• Isolation: Transactions should not affect other transactions incorrectly.

• Durability: After a transaction is committed, it should be stored in such a way that if something happens to the system later on, you still have this change.
  The very first topic you need to prepare for in DBMS interview questions is ACID properties.

What Is Data Integrity?

Data integrity refers to the accuracy, consistency, and reliability of data in storage, processing, or transit. Database constraints like primary key, foreign key, unique constraint, and check constraint help maintain the integrity of data. A primary key acts as a unique identifier that stops two records from having the same key value.

What Is a NULL Value?

NULL: It specifies no value or an unknown value. This is not exactly 0 or an empty string.
We may have NULL in the field, for example, if we want to store a customer's phone number and we don't have the customer's phone number available, then that field can be NULL.
Null Handling is Important – NULL comparisons require special SQL like IS NULL or IS NOT NULL.

What Is a View?

A view is a virtual table taken from the output of a query.
A traditional database view holds the definition of a query, rather than a separate copy of the underlying data.
Views are useful in simplifying complex queries, and they can also restrict access to certain data for users.

What Is a Stored Procedure?

Stored procedures are SQL statements that are stored in a database and run on demand.
Stored procedures come in handy for frequently repeated operations on a database and encapsulating some part of the logic around your database.
Features and syntax will be similar but not identical between database systems.

What Is a Deadlock?

A deadlock is a situation where two or more transactions wait for resources by each other and hence cannot proceed.
For example, Transaction A has Resource 1 and is waiting for Resource 2 while Transaction B has Resource 2 and waits for Resource 1.
There are various techniques employed by different database systems either to detect, prevent, or recover from deadlocks.

Difference between DELETE, DROP and TRUNCATE?

These commands have different purposes.

• DELETE — If you want to delete rows from a table, DELETE is used, and it can be applied with any WHERE condition

• TRUNCATE — It deletes all the rows of a table and can be used when one needs to clear out the entire data of the table.

• DROP removes the database object itself (like DROP TABLE).
  It is crucial to distinguish between these two commands, as they do not operate in the same way.

DBMS Interview Questions: How to Be Selectively Ready

Good preparation is not just about memorising definitions. It is best to start off by understanding basic concepts of tables, keys, relationships, normalisation, SQL, and transactions.
It is also good to practise SQL queries on a regular basis. Practice SQL queries that use SELECT, WHERE, GROUP BY, ORDER BY, JOIN, subqueries, and aggregate functions.
Having experience, you may be able to face practical questions like optimisation and indexing databases, transactions and concurrency, as well as database design questions from the interviewers. So, link theory with practical examples.

Final Thoughts

Common DBMS Interview Questions are the potential answers to getting a solid ground for the technical interviews. Try understanding why a concept of the database is used as opposed to searching its definition.
Use this as your test score, practise SQL regularly, and stick to the fundamental surface of the technology and table and relationship working. Majoraotika becomes higher when you focus on advanced concepts like normalisation, indexing, transactions, and concurrency optimisation.

Candidates who want to strengthen their database skills can explore an Online DBMS Course to build practical knowledge of SQL, database design, normalization, and other essential DBMS concepts.

DBMS is one of them, and if you have consistent practice and understand the basics of DBMS, then whether you are a fresher or an experienced candidate, you can easily face DBMS-related interview questions.