Top 30 SQL Interview Questions for Freshers [2024] 

For freshers interested in programming, SQL is one of the most popular programming languages that top companies are currently hiring for. And in most roles, SQL skills are almost indispensable, given that RDBMS (Relational Database Management System) is amongst the most popular databases. So, if you’re vying for a high-paying job as a fresher, it is important to prepare for your interview well. 

In this article, we’ll take you through 30 of the most commonly asked SQL interview questions for freshers. We’ve shared these SQL developer interview questions for freshers with tips on how to answer each of them. These SQL interview questions for freshers with answers have been divided based on basic concepts, selecting and manipulating data and advanced concepts. 

Let’s get started. 

Top SQL Interview Questions for Freshers: Basic Concepts 

Here are the top SQL interview questions for freshers based on basic concepts. 

Q1. What is SQL? (Structured Query Language) 

• Briefly define SQL as a language for interacting with relational databases. 
• Mention its key functionalities: storing, retrieving, manipulating, and managing data. 
• Emphasise its role in various applications like web development, data analysis, and business intelligence. 

Q2. What are the different types of SQL statements? (SELECT, INSERT, UPDATE, DELETE) 

• Explain each statement’s purpose: 

• SELECT retrieves data from tables. 
• INSERT adds new data to a table. 
• UPDATE modifies existing data in a table. 
• DELETE removes data from a table. 

• Briefly mention other types like CREATE for creating tables and DROP for removing them. 

Q3. What is a database schema? (Structure of tables) 

• Define a schema as the blueprint of a database, describing its tables, columns, and relationships. 
• Explain how it ensures data integrity and consistency. 
• Briefly mention common schema design principles like normalisation. 

Q4. What is the difference between primary key and foreign key? (Referential integrity) 

• Define a primary key as a unique identifier for each row in a table. 
• Explain how it enforces uniqueness and prevents duplicate data. 
• Define a foreign key as a column referencing the primary key of another table, establishing relationships. 
• Explain how foreign keys maintain data consistency across tables. 

Q5. What are JOINs? Explain different types of JOINs. (INNER, LEFT, RIGHT, FULL OUTER) 

• Describe JOINs as a way to combine data from multiple tables based on matching values. 
• Explain the concept of join conditions and how they filter matching rows. 
• Briefly explain different types of JOINs: 

• INNER JOIN: Returns only rows with matching values in both tables. 
• LEFT JOIN: Returns all rows from the left table and matching rows from the right table. 
• RIGHT JOIN: Returns all rows from the right table and matching rows from the left table. 
• FULL OUTER JOIN: Returns all rows from both tables, regardless of matching values. 

Q6. What is the difference between WHERE and HAVING clauses? (Filtering data) 

• Explain WHERE clause filters data before aggregation, applied to individual rows. 
• Explain HAVING clause filters data after aggregation, applied to groups of rows. 

• Give examples: 

• WHERE Salary > 50000 (filters individual rows with salary above 50000). 
• HAVING COUNT(*) > 10 (filters groups with more than 10 rows). 

Q7. What are aggregate functions? Give examples. (COUNT, SUM, AVG, MAX, MIN) 

• Define aggregate functions as calculations applied to groups of data. 
• List common examples and their usage: 

• COUNT: Number of rows in a group. 
• SUM: Total value of a column in a group. 
• AVG: Average value of a column in a group. 
• MAX: Largest value of a column in a group. 
• MIN: Smallest value of a column in a group. 

Q8. What is an alias? How are they used? (Assigning temporary names to tables or columns) 

• Define an alias as a temporary name given to a table or column for readability. 
• Explain how aliases improve query clarity and make them easier to understand. 
• Give an example: SELECT Salary AS ‘Employee Earnings’ FROM Employees 

Q9. How do you write comments in SQL? (Single-line and multi-line) 

• Explain single-line comments using — before the text. 
• Explain multi-line comments using /* and */ to encapsulate the comment. 
• Emphasise the importance of commenting for code clarity and understanding. 

Q10. What are subqueries? (Nested queries) 

• Define subqueries as queries nested within another query. 
• Explain their use for complex filtering or data retrieval. 
• Give a simple example: SELECT CustomerID FROM Orders WHERE OrderDate IN (SELECT OrderDate FROM Orders WHERE CustomerID = 123) 

Top SQL Interview Questions and Answers for Freshers: Selecting and Manipulating Data 

Here are the top SQL interview questions and answers for freshers focusing on selecting and manipulating data: 

Q11. How do you select all records from a table? 

• Use the SELECT * statement, where the asterisk (*) represents all columns. 
• Example: SELECT * FROM Customers 

Q12. How do you select specific columns from a table? 

• List the desired column names after SELECT. 
• Separate column names with commas. 
• Example: SELECT CustomerName, EmailAddress FROM Customers 

Q13. How do you select records based on certain conditions? 

• Use the WHERE clause to specify conditions. 
• You can use comparison operators like =, >, <, >=, <=, <>, and logical operators like AND, OR, NOT. 
• Example: SELECT * FROM Orders WHERE OrderDate > ‘2023-12-31’ 

Q14. How do you sort data in ascending or descending order? 

• Use the ORDER BY clause followed by the column name(s). 
• Use ASC for ascending order and DESC for descending. 

• Example: SELECT * FROM Products ORDER BY Price DESC 

Q15. How do you limit the number of results returned? 

• Use the LIMIT clause followed by the desired number of results. 
• Example: SELECT * FROM Customers LIMIT 10 

Q16. How do you filter data based on groups and perform aggregate calculations? 

• Use the GROUP BY clause to group data by specific columns. 
• Use aggregate functions like COUNT, SUM, AVG, MAX, MIN with GROUP BY. 
• Example: SELECT Country, COUNT(*) FROM Customers GROUP BY Country 

Q17. How do you update data in a table? 

• Use the UPDATE statement followed by the table name and the set of changes. 
• Specify the WHERE clause to target specific rows. 
• Example: UPDATE Products SET Price = Price * 1.1 WHERE Category = ‘Electronics’ 

Q18. How do you delete records from a table? 

• Use the DELETE statement followed by the table name and the WHERE clause. 
• Be cautious with DELETE as it is permanent. 
• Example: DELETE FROM Orders WHERE OrderStatus = ‘Canceled’ 

Q19. How do you join two tables with related data? 

• Use JOIN clauses like INNER JOIN, LEFT JOIN, RIGHT JOIN, or FULL OUTER JOIN. 
• Specify the join conditions with ON clause, comparing columns across tables. 
• Example: SELECT c.CustomerName, o.OrderID FROM Customers c INNER JOIN Orders o ON c.CustomerID = o.CustomerID 

Q20. How do you combine data from multiple tables using UNION/UNION ALL? 

• Use UNION to combine results without duplicates. 
• Use UNION ALL to combine all results including duplicates. 
• Ensure compatible column structures for combining results. 
• Example: SELECT * FROM Products WHERE Category = ‘Electronics’ UNION ALL SELECT * FROM Products WHERE Category = ‘Appliances’ 

Top SQL Interview Questions for Freshers with Answers: Advanced Concepts 

Here are the top SQL interview questions for freshers with answers based on advanced concepts: 

Q21. What are views? What are their benefits? 

• Views: Virtual tables based on pre-defined queries, providing simplified data access. 
• Benefits: Enhanced security, data abstraction, simplified complex queries, improved maintainability. 

Q22. What are stored procedures? What are their benefits? 

• Stored procedures: Pre-compiled SQL code stored in the database, improving performance and security. 
• Benefits: Reusability, modularity, reduced network traffic, improved performance, enhanced security. 

Q23. Explain the concept of normalisation in database design. 

• Normalisation: Reducing data redundancy to improve efficiency and data integrity. 
• Explain different normal forms (1NF, 2NF, 3NF) and their benefits. 

Q24. What are different data types used in SQL? 

• Explain common data types: integers, strings, dates/times, decimals, booleans, etc. 
• Briefly mention specific data types depending on the chosen SQL dialect. 

Q25. How do you handle NULL values in SQL? 

• Explain NULL representing missing data. 
• Mention functions like IS NULL, COALESCE, NVL for handling NULL values. 

Q26. What are indexes? How do they improve performance? 

• Indexes: Data structures enabling faster data retrieval. 
• Explain how they work like book indexes, speeding up searching by specific values. 

Q27. Explain the concept of transactions in SQL. 

• Transactions: Groups of SQL statements treated as a single unit, ensuring data consistency. 
• Explain ACID properties (Atomicity, Consistency, Isolation, Durability). 

Q28. How do you write simple conditional statements in SQL? 

• Explain using the CASE WHEN expression for conditional logic within queries. 
• Provide examples with multiple conditions and default values. 

Q29. What are user-defined functions (UDFs)? How are they created? 

• UDFs: Custom functions written in SQL for specific tasks. 
• Briefly explain syntax for creating UDFs (varies depending on dialect). 

Q30. Explain the basic differences between different SQL dialects (e.g., MySQL, PostgreSQL): 

• Focus on key differences in data types, functions, syntax, features. 
• Avoid deep comparisons, showcasing knowledge of general concepts. 

Remember that these SQL interview questions and answers for beginners are just examples, and specific questions may vary depending on the interviewer and role. Be prepared to write and explain your queries, emphasising clarity and efficiency. Practice SQL regularly to get comfortable with the syntax and different functionalities. 

FAQs on SQL Interview Questions for Freshers 

Q1. How can freshers prepare for SQL interviews? 

Ans: Freshers can prepare for SQL interviews by: 

• Practicing basic queries: Master SELECT, WHERE, JOIN, ORDER BY, GROUP BY, UPDATE, and DELETE. 
• Understanding core concepts: Know data types, normalisation, transactions, and NULL values. 
• Solving problems on platforms: Use platforms like HackerRank or LeetCode for practice. 
• Reviewing common questions: Study popular questions and different dialects (e.g., MySQL, PostgreSQL). 
• Practicing mock interviews: Simulate interview scenarios for confidence and clarity. 

Q2. What are the important topics in SQL for interview? 

Ans: Here are the super important topics in SQL for interviews: 

Fundamentals: 

• Basic query types (SELECT, WHERE, JOIN, GROUP BY, etc.) 
• Data manipulation (INSERT, UPDATE, DELETE) 
• Data types and NULL values 
• Joins (INNER, LEFT, RIGHT, etc.) 
• Aggregate functions (COUNT, SUM, AVG, etc.) 
• Subqueries 

Intermediate: 

• Normalisation principles 
• Indexes and performance optimisation 

• Stored procedures and functions 
• Views and data abstraction 
• Transactions and data integrity 

Advanced (depending on role): 

• Triggers and event handling 
• User-defined functions and procedures 
• Security and access control 
• Specific features of chosen SQL dialect (e.g., MySQL stored procedures vs. PostgreSQL functions) 

Q3. Are there any specific SQL concepts freshers should focus on? 

Ans: Yes! Freshers should focus on the core SQL concepts that form the foundation: 

• Query basics: Master SELECT, WHERE, JOIN, ORDER BY, etc., for data retrieval and filtering. 
• Data manipulation: Understand INSERT, UPDATE, DELETE for working with existing data. 
• Data types and NULLs: Grasp different data types and handling missing data with NULL properly. 
• Joins: Familiarise yourself with INNER JOIN, LEFT JOIN, and RIGHT JOIN for combining data effectively. 
• Aggregate functions: Master COUNT, SUM, AVG, etc., for summarising and analysing data. 
• Subqueries: Understand how to use nested queries for complex data retrieval. 

Q4. What are the typical challenges faced by freshers in SQL interviews? 

Ans: Here are some typical challenges freshers face in SQL interviews: 

Knowledge gaps: 

• Lack of understanding of core concepts like joins, subqueries, normalisation. 
• Unfamiliarity with specific SQL dialects or functionalities. 

Syntax errors and inefficiencies: 

• Mistakes in writing queries, leading to errors or suboptimal performance. 
• Difficulty optimising queries for efficient data retrieval. 

Problem-solving struggles: 

• Inability to translate real-world problems into appropriate SQL queries. 
• Difficulty tackling open-ended or scenario-based questions. 

Communication and clarity: 

• Challenges explaining thought process and query logic clearly. 
• Difficulty communicating technical concepts in a concise and understandable way. 

Nervousness and pressure: 

• Performance anxiety leading to mistakes or forgetting basic concepts. 
• Difficulty handling the interview format and time constraints. 

Q5. What are the key tips for answering SQL interview questions as a fresher? 

Ans: Here are some key tips for answering SQL interview questions as a fresher: 

• Master the basics: Drill down on SELECT, WHERE, JOIN, GROUP BY, ORDER BY etc. 
• Practice data manipulation: Get comfortable with INSERT, UPDATE, DELETE operations. 
• Understand data types & NULLs: Know data types and how to handle NULL values effectively. 
• Tackle joins confidently: Master INNER JOIN, LEFT JOIN, and RIGHT JOIN for data combination. 
• Leverage aggregates: Be familiar with COUNT, SUM, AVG etc. for data analysis. 
• Practice online: Utilise platforms like HackerRank or LeetCode to sharpen your skills.