Top 50+ SQL Interview Questions and Answers

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SQL stands for Structured Query Language. It was first developed in the 1970s by Donald D. Chamberlin and Raymond F. Boyce at IBM. Originally called SEQUEL, it was later shortened to SQL. Today, it is the standard language for managing and querying data in relational databases. SQL is used in almost every industry, from finance to healthcare. Roles like database developer, data analyst, and backend engineer rely on SQL daily. If you are applying for such jobs, reviewing common SQL interview questions and answers is a smart and practical way to prepare. This blog shares 50+ of the most frequently asked questions, along with tips to help you succeed.

Fun Fact: SQL is the 4th most used programming language in the world. According to a Statista report, nearly 51% of developers use it.

A complete guide to help you prepare for and crack the SQL interview

SQL Interview Readiness Guide

Category	Details
Job Roles	SQL Developer, Data Analyst, Backend Engineer, BI Developer
Common SQL Interview Topics	Joins, Subqueries, Indexing, GROUP BY, Window Functions, Normalization
Skill Level	Beginner to Advanced
Typical Rounds	2 to 3 (Technical, Coding Task, HR/Managerial)
Top Hiring Companies	Infosys, TCS, Capgemini, Google, IBM, Cognizant
Average Salary (India)	₹2.1 to 9 LPA  (1 to 6 years of experience)
What to Wear	Business casuals (avoid flashy colors)
What to Carry	Updated resume (2 copies), ID proof, pen and notepad, printed job description
Interview Duration	30 to 60 minutes for each round; coding tasks may take longer
Laptop Required?	Not for in-person interviews, but keep your system ready for virtual rounds
How to Prepare Last-Minute	Go through our SQL interview cheat sheet

Basic SQL Interview Questions

Here are some of the most common SQL interview questions and answers to help you get started with the basics.

1. What is the difference between SQL and MySQL?

SQL is a standard language used to manage and query data in relational databases. MySQL is an open-source database management system that uses SQL to perform operations. SQL is the language; MySQL is the tool.

2. Explain the types of SQL commands (DDL, DML, DCL, TCL, DQL).

• DDL (Data Definition Language): Used to create or modify tables (e.g., CREATE, ALTER, DROP).
• DML (Data Manipulation Language): Used to modify data (e.g., INSERT, UPDATE, DELETE).
• DCL (Data Control Language): Controls access (e.g., GRANT, REVOKE).
• TCL (Transaction Control Language): Manages transactions (e.g., COMMIT, ROLLBACK).
• DQL (Data Query Language): Used for data retrieval (e.g., SELECT).

3. What is the use of the SELECT statement in SQL?

The SELECT statement is used to fetch data from a table. It can return all columns or specific ones. You can also filter, sort, and join results using it.

4. How is the DELETE command different from TRUNCATE?

DELETE removes selected rows based on a condition. You can roll it back. TRUNCATE deletes all rows instantly and can’t be rolled back in most systems.

5. What are primary keys and foreign keys?

A primary key uniquely identifies each row in a table. A foreign key links one table to another and creates a relationship between them.

6. Explain the difference between WHERE and HAVING clauses.

WHERE filters rows before grouping. HAVING filters groups after aggregation. You use WHERE with normal conditions and HAVING with aggregate functions.

7. What are aggregate functions in SQL?

They perform calculations on a group of rows. Common ones include SUM(), AVG(), COUNT(), MIN(), and MAX().

8. What is normalization? Explain its types.

Normalization is a way to organize data in tables to avoid duplication.

• 1NF: Removes repeating groups.
• 2NF: Removes partial dependencies.
• 3NF: Removes transitive dependencies.

Note: Basic questions for SQL interview are often asked, even in experienced-level roles.

Also Read - Top 50+ MySQL Interview Questions and Answers

SQL Interview Questions for Freshers

These common SQL interview questions are great for freshers preparing for entry-level roles.

9. What is a table in SQL?

A table is a set of rows and columns where data is stored. Each row is a record, and each column holds a specific type of data like name, age, or salary.

10. How do you use the DISTINCT keyword?

The DISTINCT keyword is used to return only unique values. It removes duplicates from the result set. For example, SELECT DISTINCT city FROM customers will list each city only once.

11. What is the purpose of the GROUP BY clause?

GROUP BY is used to group rows with the same values in one or more columns. It’s often used with aggregate functions like SUM() or COUNT() to get grouped results.

12. What is a constraint? Name a few common ones.

A constraint is a rule applied to a column to control what kind of data can go into it. Common constraints include:

• NOT NULL – prevents null values
• UNIQUE – allows only unique values
• PRIMARY KEY – uniquely identifies each row
• FOREIGN KEY – links two tables
• CHECK – restricts the range of values

13. What is the default sorting order in ORDER BY?

By default, ORDER BY sorts data in ascending order (from smallest to largest). You can change it to descending using DESC.

14. Can a table have multiple foreign keys?

Yes, a table can have more than one foreign key. Each foreign key can refer to a different parent table or even different columns of the same table.

Remember: SQL interview topics for freshers often include basic queries, joins, aggregate functions, and simple subqueries.

SQL Interview Questions for Experienced

Let’s go through some advanced SQL interview questions and answers commonly asked in experienced-level interviews.

15. How would you optimize a slow SQL query?

I usually start by checking the execution plan. It shows where the query is slow. I look for missing indexes, large table scans, or expensive joins. Sometimes, rewriting the query or using LIMIT helps. I also avoid using SELECT *.

16. Explain different types of joins with examples.

• INNER JOIN: Returns rows with matching values in both tables.
• LEFT JOIN: Returns all rows from the left table and matching rows from the right.
• RIGHT JOIN: Opposite of LEFT JOIN.
• FULL OUTER JOIN: Returns all rows when there’s a match in either table.

Example:

SELECT a.name, b.city  

FROM users a  

LEFT JOIN orders b ON a.id = b.user_id;  

17. What are views, and when should they be used?

A view is a virtual table created from a query. It doesn’t store data. Use views to simplify complex queries, reuse code, or limit access to specific columns.

18. How does indexing affect query performance?

Indexes make searches faster by reducing the number of rows scanned. They act like a book’s index – instead of reading everything, the engine jumps straight to the match. But too many indexes can slow down updates or inserts.

19. What are temporary tables, and how are they useful?

Temporary tables are used to store data during a session. They are useful for breaking down complex operations or holding intermediate results. They disappear when the session ends.

20. What’s the difference between correlated and non-correlated subqueries?

A non-correlated subquery runs independently of the outer query. A correlated subquery depends on the outer query for its values.

Example of correlated:

SELECT name  

FROM employees e  

WHERE salary > (SELECT AVG(salary) FROM employees WHERE department = e.department);  

Bonus: Even though we have already shared the common questions for SQL interview for experienced roles, here are a few more grouped by experience level to help you prepare better.

Also Read - Top 100 SQL Query Interview Questions and Answers

SQL Interview Questions for 2 Years Experienced

• How do you handle NULL values in SQL?
• What is the difference between CHAR and VARCHAR?
• Can you describe a time when your SQL query helped solve a business problem?
• How do you handle multiple tasks and deadlines while working with SQL reports?
• A report is returning duplicate values, how would you fix it?

SQL Interview Questions for 3 Years Experienced

• What is a CTE, and how is it used?
• What is the use of the RANK() function in SQL?
• Tell us about an instance where you improved the performance of a complex query.
• How do you approach debugging a failing SQL job?
• A business user complains about missing data in their dashboard – how would you investigate?

SQL Interview Questions for 5 Years Experienced

• How do you manage schema changes in a live database?
• Explain the concept of database partitioning.
• Share a time when your SQL knowledge impacted a cross-functional project.
• How do you mentor juniors on best practices in SQL?
• You notice high CPU usage during peak query loads – what would you check?

SQL Interview Questions for 10 Years Experienced

• How do you plan a SQL migration from on-prem to cloud?
• How do you manage SQL performance across multiple environments?
• What is the most challenging database problem you have solved using SQL?
• How do you handle disagreements on database design in a team?
• A legacy system relies on poorly written stored procedures. How would you refactor them?

Also Read - Top 25+ SQL DBA Interview Questions and Answers

Advanced SQL Interview Questions

Now, let’s look at some of the toughest SQL interview questions that are often asked to test your deep understanding and problem-solving skills.

21. Explain window functions and give examples.

Window functions perform calculations across rows related to the current row. Unlike aggregate functions, they don’t collapse results into one row.

Example:

SELECT name, salary, RANK() OVER (ORDER BY salary DESC) AS rank  

FROM employees;  

This gives each employee a salary rank.

22. What is a materialized view, and when should you use one?

A materialized view stores the actual data from a query. It is helpful when the base query is heavy and doesn’t need real-time data. Use it when speed matters more than freshness.

23. What are ACID properties in SQL transactions?

• Atomicity: All steps succeed or none do.
• Consistency: Data stays valid before and after a transaction.
• Isolation: Transactions don’t interfere with each other.
• Durability: Once committed, changes remain even after a crash.

24. What is query execution plan and how do you read it?

A query execution plan shows how the database runs your query. It helps spot slow parts, like full table scans or missing indexes. You read it from right to left, starting with the deepest operation. Look at cost, row count, and join types.

25. How do you avoid deadlocks in SQL?

To avoid deadlocks:

• Access tables in the same order in all transactions.
• Keep transactions short.
• Avoid holding locks for long.
• Commit changes quickly.

I always check the error logs and retry logic when I hit a deadlock.

SQL Coding Interview Questions

Interviewers often ask SQL program questions to check your ability to write queries and solve real-time problems using code. Here are some common coding questions you might face in SQL interviews.

26. Write a SQL query to find the second highest salary from an employee table.

SELECT MAX(salary) AS second_highest

FROM employees

WHERE salary < (SELECT MAX(salary) FROM employees);

27. Write a query to find duplicate values in a column.

Example: finding duplicate emails

SELECT email, COUNT(*)

FROM users

GROUP BY email

HAVING COUNT(*) > 1;

28. Retrieve all departments with more than 5 employees.

SELECT department_id, COUNT(*) AS total_employees

FROM employees

GROUP BY department_id

HAVING COUNT(*) > 5;

29. Get the employee(s) with the highest salary in each department.

SELECT e.*

FROM employees e

JOIN (

  SELECT department_id, MAX(salary) AS max_salary

  FROM employees

  GROUP BY department_id

) d ON e.department_id = d.department_id AND e.salary = d.max_salary;

30. Find the employees who didn’t clock in today.

Assume the following two tables

1. Employees

id	name	department_id
1	John Smith	101
2	Alice Brown	102
3	Mark Taylor	101
4	Sarah Clark	103

2. Clock_in

clock_id	employee_id	date
1	1	2025-07-17
2	3	2025-07-17

SQL Query:

SELECT e.*

FROM employees e

WHERE e.id NOT IN (

  SELECT employee_id

  FROM clock_in

  WHERE date = CURRENT_DATE

);

Tip: In SQL interview questions programming, interviewers often tweak table names, column names, or data formats to see if you are thinking or just memorizing. So, focus on understanding query logic, not just syntax.

SQL Interview Questions for Common Roles

Here are role-specific questions for SQL interview to help you prepare based on the job you are applying for.

Interview Questions for SQL Data Analyst

31. How do you clean messy data in SQL?

I use functions like TRIM() to remove extra spaces, NULLIF() to fix blanks, and CAST() to convert types. I also check for inconsistent values using GROUP BY or LIKE.

32. What is your approach to validating a large data set?

First, I check row counts and data types. Then I compare summaries using COUNT(), SUM(), or AVG(). I sometimes write test queries to match source and target data. If needed, I use EXCEPT to find mismatches.

33. How would you join transactional and dimension tables?

Usually with an INNER JOIN on the key column. 

For example, join sales.transaction_id with customers.customer_id. I always check for duplicates in the dimension table first.

34. Write a query to calculate month-over-month growth.

SELECT month,

       sales,

       LAG(sales) OVER (ORDER BY month) AS prev_month,

       ROUND(((sales – LAG(sales) OVER (ORDER BY month)) / 

              NULLIF(LAG(sales) OVER (ORDER BY month), 0)) * 100, 2) AS mom_growth

FROM sales_data;

35. How do you handle outliers using SQL?

I use the PERCENTILE_CONT() or manual IQR method.

Example: filter values below Q1 – 1.5IQR or above Q3 + 1.5IQR.

Sometimes, I just flag them instead of removing.

Interview Questions for SQL Developer

Here are some of the most commonly asked interview questions for SQL Developer roles.   

36. What is the difference between stored procedure and function?

A stored procedure can return multiple values and doesn’t need to return anything. A function must return a single value. Also, functions can be used in SELECT queries, but procedures cannot.

37. How do you handle exceptions in SQL?

In systems like SQL Server or Oracle, I use BEGIN TRY…END TRY and BEGIN CATCH…END CATCH blocks. Inside the catch, I log the error and stop or roll back the transaction.

38. How do you use triggers in SQL?

Triggers are actions that run automatically when a specific event happens, like INSERT, UPDATE, or DELETE. I usually use them for auditing changes or enforcing business rules.

39. How do you schedule recurring jobs in SQL?

In SQL Server, I use SQL Server Agent. In PostgreSQL, I use pg_cron. I set the job, timing, and query. It runs automatically. I always test it first manually.

40. What is dynamic SQL? Where is it used?

Dynamic SQL is built and run as a string at runtime. It’s useful when column names, table names, or conditions are not known in advance. I have used it in reporting tools and automation scripts.

Also Read - Top 25+ PostgreSQL Interview Questions and Answers

Topic-Based SQL Interview Questions

Now, let’s take look at SQL interview questions grouped by specific topics like joins, indexes, T-SQL, and more for targeted preparation.

Interview Questions on Join in SQL

1. Difference between INNER JOIN and LEFT JOIN.
2. When would you use FULL OUTER JOIN?
3. What is a CROSS JOIN?
4. How do you join three or more tables?
5. Explain self-join with an example.

NoSQL Interview Questions

1. What is the difference between SQL and NoSQL databases?
2. Explain CAP theorem in NoSQL.
3. What are document-based NoSQL databases?
4. Use cases for choosing NoSQL over SQL?
5. Can NoSQL databases support joins?

ANSI SQL Interview Questions

1. What is ANSI SQL?
2. Difference between ANSI SQL and T-SQL?
3. What are standard SQL data types?
4. What does ANSI compliance mean?
5. Which database vendors follow ANSI SQL?

Index in SQL Interview Questions

1. What is an index and why use it?
2. Difference between clustered and non-clustered index?
3. Can a table have multiple indexes?
4. What is a composite index?
5. When should you avoid using indexes?

Azure SQL Interview Questions

1. What is Azure SQL Database?
2. Difference between Azure SQL and SQL Server. 
3. How do you scale Azure SQL?
4. What are DTUs and vCores in Azure SQL?
5. How is geo-replication handled in Azure SQL?

MS SQL Interview Questions

1. What is SQL Server Management Studio (SSMS)?
2. How do you back up and restore a database in SQL Server?
3. Explain the use of TempDB in MS SQL.
4. What are SQL Server Agent jobs?
5. What is SQL Profiler?

Also Read - Top 50+ SQL Server Interview Questions and Answers

Interview Questions on T SQL

1. What is T-SQL?
2. Difference between T-SQL and SQL.
3. How do you declare variables in T-SQL?
4. How do you write a loop in T-SQL?
5. What is TRY-CATCH in T-SQL?

Java SQL Interview Questions

1. How do you connect a SQL database using JDBC?
2. What are prepared statements in Java SQL?
3. How do you handle SQL exceptions in Java?
4. How do you execute a stored procedure in Java?
5. What libraries can help manage SQL queries in Java?

Also Read - Top 20 JDBC Interview Questions and Answers

Production Support SQL Interview Questions

1. How do you monitor long-running SQL queries?
2. How do you roll back a failed transaction?
3. What is a blocking session, and how do you fix it?
4. How do you audit database changes?
5. What is your process for troubleshooting deadlocks?

Top SQL Interview Questions Asked By the Top IT Companies

Here are some of the most common and tricky SQL questions asked by leading IT companies during technical interviews. Use them to understand what top recruiters expect.

Capgemini SQL Interview Questions

1. Write a query to fetch top 3 highest salaries.
2. Explain CTE with an example.
3. What is the difference between DELETE and TRUNCATE?
4. How do you handle NULLs in JOINs?
5. What is normalization?

IBM SQL Interview Questions

1. What is indexing in SQL?
2. Difference between WHERE and HAVING.
3. How to retrieve 5th highest salary?
4. Write a query to pivot table rows to columns.
5. Explain the use of ROWNUM.

Tech Mahindra SQL Interview Questions

1. What are ACID properties?
2. How do you optimize a slow query?
3. Difference between IN and EXISTS.
4. Write a query to find employee with duplicate email.
5. What is a surrogate key?

Cognizant SQL Assessment Questions

1. What is a trigger?
2. Difference between stored procedure and function.
3. How to perform error handling in SQL?
4. What is data truncation?
5. What is the use of MERGE statement?

Hexaware SQL Interview Questions

1. Explain different types of normalization.
2. Write a query to count rows in each group.
3. What is a composite key?
4. How to delete duplicate rows?
5. Explain the difference between RANK and DENSE_RANK.

Informatica SQL Interview Questions

1. What are OLTP and OLAP systems?
2. What is surrogate key? When do you use it?
3. Difference between UNION and UNION ALL.
4. How do you join more than two tables?
5. What is SCD (Slowly Changing Dimension)?

SQL Interview Questions for Infosys

1. Explain the difference between BETWEEN and IN.
2. Write a query to find the department with max salary.
3. What is normalization? Explain 1NF and 2NF.
4. How do you use CASE statement?
5. How to update one table using data from another?

Walmart SQL Interview Questions

1. What is a covering index?
2. How would you analyze sales data using SQL?
3. Write a query to calculate running totals.
4. What is the use of WINDOW functions?
5. What is the difference between PARTITION BY and GROUP BY?

Google SQL Interview Questions

1. What are BigQuery’s limitations compared to traditional SQL?
2. How do you write optimized SQL for large datasets?
3. What is a WITH clause and how do you use it?
4. How do you filter NULLs in aggregation?
5. How do you test performance of queries at scale?

Note: These company-specific SQL interview questions are compiled from commonly reported interview experiences and top preparation resources. While not officially confirmed, they reflect the typical patterns seen in interviews at these companies.

SQL MCQ Questions

These are some SQL questions for practice in multiple-choice format to help you test your knowledge and get ready for interviews.

1. What does the SQL acronym stand for?

A) Simple Query Language
B) Structured Question Language
C) Structured Query Language
D) System Query Language

Answer: C) Structured Query Language

2. Which clause is used to sort results in SQL?

A) GROUP BY
B) ORDER BY
C) SORT
D) ARRANGE BY

Answer: B) ORDER BY

3. Which SQL statement is used to insert data?

A) ADD
B) INSERT INTO
C) PUT
D) UPDATE

Answer: B) INSERT INTO

4. What does the COUNT(*) function do?

A) Counts only NULL values
B) Counts only distinct values
C) Counts all rows including NULLs
D) Counts rows without NULLs

Answer: C) Counts all rows including NULLs

5. Which statement is used to delete a table?

A) DROP TABLE
B) REMOVE TABLE
C) DELETE TABLE
D) ERASE TABLE

Answer: A) DROP TABLE

6. Which command is used to retrieve data?

A) GET
B) EXTRACT
C) SELECT
D) FETCH

Answer: C) SELECT

7. What is the default sort order in ORDER BY?

A) DESC
B) ASC
C) Random
D) None

Answer: B) ASC

8. Which constraint stops null values in a column?

A) UNIQUE
B) CHECK
C) PRIMARY KEY
D) NOT NULL

Answer: D) NOT NULL

9. Which function gives current date and time?

A) CURRENT_DATE
B) GETDATE()
C) NOW()
D) SYSDATE()

Answer: C) NOW() (for MySQL/PostgreSQL; use GETDATE() for SQL Server and SYSDATE for Oracle)

10. Which command is used to remove duplicates?

A) SELECT UNIQUE
B) DELETE DUPLICATES
C) SELECT DISTINCT
D) REMOVE DUPLICATE

Answer: C) SELECT DISTINCT

SQL Interview Cheat Sheet

Topic	Key Points
SQL Full Form	Structured Query Language
Basic Commands	SELECT, INSERT, UPDATE, DELETE, CREATE, DROP
Joins	INNER, LEFT, RIGHT, FULL OUTER — used to combine data from tables
Clauses	WHERE (filter rows), HAVING (filter groups), GROUP BY, ORDER BY
Constraints	NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, CHECK
Aggregate Functions	COUNT(), SUM(), AVG(), MIN(), MAX()
Window Functions	ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD()
Subqueries	Correlated (depends on outer query) vs. Non-correlated (independent)
Indexes	Speeds up data retrieval, but slows down insert/update
Views	Virtual tables based on SQL queries
Stored Procedure	Precompiled SQL block; can return multiple values
Function	Returns a single value; can be used inside a SELECT
Normalization	Process to reduce data redundancy (1NF, 2NF, 3NF)
ACID Properties	Atomicity, Consistency, Isolation, Durability
Temp Tables	Exist temporarily during a session or transaction
Materialized View	Stores actual data; faster reads, slower updates
Common Interview Tip	Practice real queries; focus on logic, not just syntax

Tips to Prepare for SQL Interview

Preparing well can make a huge difference in how you answer technical SQL questions confidently. Here are some tips you can follow:

• Focus on core SQL interview topics like joins, subqueries, and window functions
• Practice writing queries daily using real problems
• Solve common SQL questions for practice from online platforms
• Review recent questions for SQL interview asked by top companies
• Understand query logic instead of memorizing syntax
• Read and analyze sample execution plans

Wrapping Up

So, here are the 50+ SQL interview questions and answers to help you prepare better. Go through them, practice writing queries, and focus on understanding each concept clearly. Solid basics and hands-on skills go a long way.

Looking for SQL jobs? Head over to Hirist, where you can find top IT openings, including SQL developer and analyst roles.

FAQs

SQL Developer Salary Overview (India, 2025)

Metric	Value
Annual salary range	₹2.1 Lakhs – ₹9 Lakhs
Avg. annual salary	₹5.1 Lakhs
Monthly in-hand salary	₹33,000 – ₹35,000
Experience range in data	1 – 6 years

Salary by Experience

Experience	Average Annual Salary
1 year	₹3.4 Lakhs per year
2 years	₹4.2 Lakhs per year
3 years	₹5.2 Lakhs per year
4 years	₹6.4 Lakhs per year

Salary by City

City	Average Annual Salary
Gurgaon	₹6.3 Lakhs per year
Noida	₹5.5 Lakhs per year
New Delhi	₹5.4 Lakhs per year
Bangalore	₹5.4 Lakhs per year
Hyderabad	₹5.4 Lakhs per year

Top Paying Companies for SQL Developers

Company	Average Annual Salary
AvenData GmbH	₹6.4 Lakhs per year
Genpact	₹6.3 Lakhs per year
Corecard Software	₹5.9 Lakhs per year
Accenture	₹5.8 Lakhs per year
Deloitte	₹5.2 Lakhs per year