RDBMS stands for Relational Database Management System. It helps store and manage data using tables. The idea was introduced by Edgar F. Codd at IBM in the 1970s. His model changed the way data was handled and is still used today in systems like MySQL, Oracle, and SQL Server. If you are heading into a tech interview, chances are you will face questions on RDBMS – especially around queries, normalization, and relationships. This blog brings together 20+ commonly asked interview questions for RDBMS, along with expert-level answers to help you understand the concepts and get ready for your interview.
Fun Fact – According to Statista, Oracle is the most popular RDBMS in the world.
Note – We have grouped the interview questions for RDBMS into basic, intermediate, and advanced levels to make your preparation easier and clearer.
Basic Level Interview Questions for RDBMS
Here are some commonly asked basic-level interview questions on RDBMS that test your fundamental understanding of databases and their core concepts.
- What is an RDBMS and how is it different from a DBMS?
An RDBMS (Relational Database Management System) stores data in structured tables with rows and columns. It supports relationships between tables using keys like primary and foreign keys.
A DBMS (Database Management System) is a broader term that refers to any system that stores data. It doesn’t always use tables or support relationships.
RDBMS follows the relational model and supports multiple related tables, while DBMS may only handle single files or flat data.
- What is the difference between a primary key and a unique key?
A primary key uniquely identifies each record and cannot have null values. Each table can have only one. A unique key also prevents duplicates but allows one null value. You can have multiple unique keys in a table.
- Can a table have more than one foreign key?
Yes, it can. A table may refer to multiple other tables using different foreign keys. Each foreign key links to a primary or unique key in another table.
- What is normalization and why is it important?
Normalization is a method to organize data in tables to avoid redundancy. It reduces data repetition and makes updates easier. It also helps maintain consistency.
- What are the different types of joins in SQL?
There are four main joins:
- INNER JOIN returns matching records.
- LEFT JOIN returns all rows from the left, and matches from the right.
- RIGHT JOIN returns all rows from the right, and matches from the left.
- FULL JOIN returns all records from both tables.
- Explain the difference between DELETE and TRUNCATE commands.
DELETE removes rows one by one and can be rolled back. You can also apply a condition. TRUNCATE removes all rows quickly and can’t be rolled back in most systems. It resets identity counters too.
- What is a foreign key and why is it used?
A foreign key is a column that links to the primary key of another table. It creates a relationship between two tables and helps maintain referential integrity. This means you can’t insert a value in the foreign key column if it doesn’t exist in the parent table.
Intermediate Level Interview Questions for RDBMS
These are intermediate-level RDBMS questions and answers that help you build a deeper understanding of joins, normalization, keys, and practical database use.
- What is a composite key and when should you use one?
A composite key is made up of two or more columns that together make a row unique. Use it when no single column can uniquely identify records.
- How does indexing improve database performance?
Indexes let the database find data faster by creating a lookup structure. Without indexes, a query scans every row, which is slower on large tables.
- What is a subquery? How is it different from a join?
A subquery is a query inside another query. It runs first and returns a value. A join combines rows from two or more tables. Subqueries work like filters. Joins merge data.
- Explain the concept of ACID properties in RDBMS.
ACID stands for:
- Atomicity – a transaction is all or nothing.
- Consistency – data moves from one valid state to another.
- Isolation – each transaction runs as if it’s alone.
- Durability – once done, it stays done even if the system crashes.
- What are the anomalies that normalization helps to avoid?
Normalization avoids:
- Insertion anomaly – trouble adding data.
- Update anomaly – need to change data in many places.
- Deletion anomaly – losing valuable data when deleting unrelated info.
- What is the difference between WHERE and HAVING in SQL?
WHERE filters rows before grouping, while HAVING filters after grouping. Use WHERE for raw data and HAVING for aggregates like COUNT or SUM. For example, you can’t use HAVING without a GROUP BY clause in most cases.
- Can you describe a time when you used normalization in a real project?
Yes. In a library project, I noticed author names were repeated with every book entry. I applied normalization and moved authors to a separate table. This reduced redundancy and made updates easier. It also helped me understand how clean design improves data handling.
Advanced Level Interview Questions for RDBMS
Let’s go through the important advanced-level relational database management system questions and answers.
- What is a clustered index vs a non-clustered index?
A clustered index decides how data is physically stored. Each table can have only one. A non-clustered index is separate from the data and stores pointers. You can have many of these.
- How do transactions work in multi-user environments?
Databases use locks and isolation levels to keep transactions safe. If two users try to change the same row, one waits or fails. Isolation levels help balance speed and accuracy.
- What is query optimization and how does it work in RDBMS?
Query optimization finds the fastest way to run a query. The database checks different plans and chooses the most efficient one based on table size, indexes, and joins.
- How does RDBMS handle deadlocks and how can they be avoided?
Deadlocks happen when two transactions wait for each other’s locks. RDBMS systems detect them and kill one to let the other finish. You can avoid them by accessing tables in a fixed order, keeping transactions short, and using proper indexing.
- What’s the difference between horizontal and vertical partitioning in databases?
Horizontal partitioning splits a table into rows—like separating data by region. It’s good for large datasets. Vertical partitioning splits it into columns—useful for reducing data loaded at once. Both help with performance and maintenance.
- What is a transaction log and why is it important?
A transaction log records all changes made to the database. It’s used for recovery in case of a crash. If something fails mid-transaction, the log helps roll back incomplete changes or reapply committed ones.
RDBMS Interview Questions for Freshers
Here is a list of beginner-friendly RDBMS interview questions to help freshers build confidence and cover the basics.
- What is the difference between DBMS and RDBMS?
- What is a table in RDBMS?
- What is a candidate key?
- Define the concept of referential integrity.
- What is the role of SQL in an RDBMS?
Interview Questions on RDBMS for Experienced Professionals
These interview questions on RDBMS are for experienced candidates tackling real-world scenarios and in-depth concepts.
- How do you handle slow-running queries in large RDBMS systems?
- What is denormalization and when would you use it?
- How do you design a relational schema for a complex system?
- What are materialized views and how do they differ from regular views?
- What steps do you take to tune a relational database for high performance?
How to Prepare for RDBMS Interview
Here are some practical tips to help you prepare for your RDBMS interview.
- Understand core concepts – Know what RDBMS is, how tables relate, and why keys matter.
- Practice SQL daily – Focus on SELECT, JOINs, GROUP BY, and subqueries. Write queries, don’t just read them.
- Use sample schemas – Work with real or sample datasets like employee or library databases to test your skills.
- Learn by solving problems – Use coding platforms or interview prep sites with SQL challenges.
- Mock interviews help – Practice answering out loud with a friend or in front of a mirror.
- Read real interview questions – Focus on common interview questions for RDBMS asked by companies.
Also Read - Top 100 SQL Query Interview Questions and Answers
Wrapping Up
These 20+ interview questions for RDBMS cover the most important topics you are likely to face in real interviews. From keys and joins to transactions and indexing, each answer helps you build a strong foundation.
Looking for RDBMS jobs? Visit Hirist – an online job portal for IT professionals. Here, you can find the top RDBMS job openings in India quickly and easily.
FAQs
What are the 4 types of RDBMS?
The four types of RDBMS are:
- Hierarchical RDBMS – Stores data in a tree structure, where each child has one parent.
- Network RDBMS – Supports many-to-many relationships using linked records.
- Object-oriented RDBMS – Combines object-oriented features with relational tables, useful for complex data types.
- Relational RDBMS – The most widely used type; stores data in tables and uses SQL for querying.
Most modern systems use the relational model.
What are the RDBMS important questions to prepare for interviews?
RDBMS important questions usually cover primary keys, foreign keys, normalization, types of joins, ACID properties, indexing, and SQL queries. Focus on both basic theory and practical query writing.
What is the average salary for RDBMS professionals in India?
The average salary for RDBMS professionals in India is around ₹24.2 lakhs per year. Most earn between ₹17.1 lakhs and ₹76 lakhs annually. The top 10% of professionals make over ₹39.7 lakhs a year.
Which top companies hire for RDBMS-related roles?
Top companies hiring RDBMS experts include TCS, Infosys, Wipro, Accenture, Oracle, IBM, and product-based firms like Zoho, Freshworks, and Razorpay.
