Placement Prep

SQL and DBMS for Placement Preparation: What You Must Know in 2026

SQL and DBMS preparation for campus placements in 2026. Topics, important queries, normalization, and interview questions for B.Tech, BCA, MCA freshers.

Classroom Tech Updated 3 min read

SQL and DBMS appear in virtually every technical interview — service companies, product companies, and even AI roles. This guide covers exactly what to prepare.

Why DBMS Is Always Asked

  1. Almost every software system uses a database
  2. It tests your understanding of data management fundamentals
  3. SQL writing ability separates developers who can ship from those who can't

DBMS Theory: Key Topics for Interviews

Fundamentals

  • What is a DBMS? DBMS vs file system
  • Keys: primary key, foreign key, candidate key, super key, composite key
  • Relationships: one-to-one, one-to-many, many-to-many
  • ER diagrams — know how to draw and interpret them

Normalization

  • 1NF, 2NF, 3NF, BCNF — know the rules and be able to apply them
  • Functional dependencies
  • Anomalies (insert, delete, update)

Transactions

  • ACID properties (Atomicity, Consistency, Isolation, Durability)
  • Concurrency control
  • Deadlock and its handling

Indexing

  • What is an index and why it speeds up queries
  • B-tree index, hash index
  • When not to index

SQL: Must-Know Queries

Basic Queries

SELECT name, salary FROM employees WHERE department = 'IT';
SELECT DISTINCT city FROM customers;
SELECT * FROM orders ORDER BY date DESC LIMIT 10;

Joins (Most Important)

-- INNER JOIN
SELECT e.name, d.dept_name
FROM employees e
INNER JOIN departments d ON e.dept_id = d.id;

-- LEFT JOIN
SELECT c.name, o.order_id
FROM customers c
LEFT JOIN orders o ON c.id = o.customer_id;

Aggregate Functions

SELECT department, COUNT(*), AVG(salary), MAX(salary)
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;

Subqueries

SELECT name FROM employees
WHERE salary > (SELECT AVG(salary) FROM employees);

Window Functions (for product companies)

SELECT name, salary,
  RANK() OVER (PARTITION BY department ORDER BY salary DESC) as rank
FROM employees;

Top 10 DBMS Interview Questions

  1. What is normalization? Explain 1NF, 2NF, 3NF.
  2. What are ACID properties?
  3. Difference between DELETE, TRUNCATE, and DROP.
  4. What is a primary key vs foreign key?
  5. Explain different types of JOINs with examples.
  6. What is an index? When would you avoid using one?
  7. What is a view? How is it different from a table?
  8. Explain transaction management and rollback.
  9. What is a stored procedure vs a function?
  10. Write a query to find the second highest salary.

The Second Highest Salary Query (Always Asked)

SELECT MAX(salary) FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);
-- OR using LIMIT/OFFSET
SELECT salary FROM employees
ORDER BY salary DESC LIMIT 1 OFFSET 1;

About the Author & Classroom Tech

Satyaki Das is the founder of Classroom Tech and co-founder of XShare. He holds an MTech in Computer Engineering from Jadavpur University and an MCA from Techno Main, Salt Lake, Kolkata. He is a Java Full Stack Developer at TCS, a GATE-qualified engineer, and ranked 848 in Codevita — one of TCS's global coding contests. With 11+ years of teaching experience and over 11,000 LinkedIn followers, Satyaki has mentored hundreds of students from BCA, B.Tech, MCA, and working professional backgrounds into roles at TCS, Wipro, Infosys, Accenture, EY, Deloitte, and Capgemini.

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