Top 50 SQL Interview Questions With Answers: Ace Your Next Data Job!

If you're preparing for an SQL interview, you can expect questions that test your understanding of database design, query optimization, and performance tuning. Common SQL interview questions typically focus on database normalization, performance tuning, handling large datasets, and writing complex queries. 

For example, you might be asked, "How would you optimize a query involving multiple joins and large datasets?" or "What indexing strategies would you use to improve performance?" These questions assess your technical knowledge and problem-solving skills.

This blog will cover key SQL interview questions, provide expert answers, and offer helpful strategies to tackle each question. 

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SQL Interview Questions for Beginners and Freshers

If you're a beginner or fresher preparing for an SQL interview, expect questions that focus on basic concepts, such as simple queries, joins, and data manipulation. These questions will test your ability to write and understand fundamental SQL commands. 

In this section, you'll find a list of common SQL interview questions for beginners along with clear answers to help you prepare effectively. Let's go through the key topics you need to focus on.

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1. What is SQL?

How to Answer:

• Start by defining SQL as a standard programming language for managing relational databases.
• Mention its core functions: creating, retrieving, updating, and deleting data (CRUD operations).
• Highlight that SQL is used for handling structured data in relational databases.
• Emphasize its widespread use across industries for database management.
• Keep the explanation clear and concise, focusing on SQL's role in data manipulation and management.

Sample Answer:

SQL (Structured Query Language) is a standard programming language used for managing and manipulating relational databases. It allows users to create, retrieve, update, and delete data. SQL is widely used in industries for handling structured data efficiently.

2. What are the different types of SQL commands?

How to Answer:

• Start by explaining the five types of SQL commands.
• Briefly define each category.
• Keep your answer clear, concise, and focused on the purpose of each command type.

Sample Answer:

SQL commands are divided into five types:

• DDL (Data Definition Language): CREATE, ALTER, DROP (for defining structure).
• DML (Data Manipulation Language): INSERT, UPDATE, DELETE (for modifying data).
• DQL (Data Query Language): SELECT (for retrieving data).
• TCL (Transaction Control Language): COMMIT, ROLLBACK, SAVEPOINT (for transaction management).
• DCL (Data Control Language): GRANT, REVOKE (for access control).

3. What is a primary key in SQL?

How to Answer:

• Define a primary key as a unique identifier for each record in a table.
• Mention that it can consist of one or more columns.
• Emphasize that primary keys cannot have duplicate or NULL values.
• State that only one primary key can exist in a table to ensure data integrity.

Sample Answer:

A primary key is a column or a set of columns that uniquely identifies each record in a table. It does not allow duplicate or NULL values. A table can have only one primary key, ensuring data integrity.

4. What is a foreign key?

How to Answer:

• Define a foreign key as a column (or set of columns) in one table that refers to the primary key of another table.
• Explain that it creates a relationship between the two tables.
• Highlight its role in maintaining referential integrity and ensuring consistent data across tables.

Sample Answer:

A foreign key is a column or set of columns in one table that refers to the primary key of another table. It establishes a relationship between tables and ensures referential integrity. Foreign keys help maintain consistent and accurate data across multiple tables.

5. Explain the difference between DELETE and TRUNCATE commands.

How to Answer:

• Explain the differences between the commands in brief. 

Sample Answer:

• DELETE: Removes specific records based on a condition and can be rolled back using ROLLBACK.
• TRUNCATE: Removes all rows from a table but retains the structure, and it cannot be rolled back.
• DELETE is slower than TRUNCATE because it logs each deleted row.

6. What is the difference between SQL and MySQL?

How to Answer:

• Clarify that SQL is a standard language for managing databases.
• Explain that MySQL is a relational database management system (RDBMS) that uses SQL.
• SQL defines the language for querying and managing data, while MySQL is the software that handles the actual database storage and operations.

Sample Answer:

SQL is a standard language used for database management, while MySQL is a relational database management system (RDBMS) that implements SQL. SQL defines how data is manipulated, whereas MySQL provides the tools to store, retrieve, and manage that data.

7. What is normalization in SQL?

How to Answer:

• Define normalization as the process of organizing data in a database to reduce redundancy.
• Explain that it divides large tables into smaller, related tables to improve efficiency.
• Mention that normalization helps maintain data integrity and minimizes anomalies.

Sample Answer:

Normalization is the process of organizing a database to reduce redundancy and improve efficiency. It divides large tables into smaller related tables and establishes relationships between them. This improves data integrity and reduces data anomalies.

8. What are joins in SQL? Name the different types.

How to Answer:

• Define joins as operations used to combine data from multiple tables based on a related column.
• List the types of joins.

Sample Answer:

Joins are used to retrieve data from multiple tables based on a related column. The different types of joins are:

• INNER JOIN: Returns records with matching values in both tables.
• LEFT JOIN: Returns all records from the left table and matching records from the right.
• RIGHT JOIN: Returns all records from the right table and matching records from the left.
• FULL JOIN: Returns all records when there is a match in either table.

Also Read: SQL for Data Science: Functions, Queries, and Best Practices

9. What is the difference between WHERE and HAVING clauses?

How to Answer:

• Explain the differences between these two one by one. 

Sample Answer:

• WHERE: Filters rows before performing aggregation (used with SELECT, UPDATE, DELETE).
• HAVING: Filters rows after aggregation (used with GROUP BY).
• WHERE works on individual records, while HAVING works on grouped data.

10. What is an index in SQL?

How to Answer:

• An index is a database object that improves data retrieval speed by creating a pointer to the records.
• It works similarly to an index in a book, allowing faster searches.
• Keep in mind that indexes can slow down INSERT, UPDATE, and DELETE operations because they must be updated whenever data changes.

Sample Answer:

An index is a database object that speeds up data retrieval operations by creating a pointer to records. It works like a book index, allowing the database to find specific data quickly. However, indexes can slow down INSERT, UPDATE, and DELETE operations because they need to be updated.

11. What is the difference between UNIQUE and PRIMARY KEY constraints?

How to Answer:

Explain the differences between these two one by one. 

Sample Answer:

• PRIMARY KEY: Ensures uniqueness and does not allow NULL values. A table can have only one primary key.
• UNIQUE: Ensures uniqueness but allows NULL values. A table can have multiple unique constraints.

12. What is a stored procedure in SQL?

How to Answer:

• A stored procedure is a set of SQL statements stored in the database and executed as a single unit.
• It improves performance by reducing repeated execution of the same code.
• Stored procedures also enhance security by restricting direct data access.

Sample Answer:

A stored procedure is a collection of SQL statements that are stored in the database and executed as a single unit. It helps improve performance by reducing repeated code execution and enhancing security by restricting direct access to data.

13. What is the difference between CHAR and VARCHAR data types?

How to Answer:

Explain the differences between these two one by one. 

Sample Answer:

CHAR is a fixed-length data type that stores strings of a defined length, while VARCHAR is a variable-length data type that stores strings with flexible lengths. CHAR is faster for fixed-size data, whereas VARCHAR is more space-efficient for variable-length text.

14. What is a NULL value in SQL?

How to Answer:

• Define NULL as representing missing or unknown data.
• Differentiate NULL from zero or an empty string.
• Mention SQL functions to handle NULL, such as IS NULL and IS NOT NULL.

Sample Answer:

A NULL value in SQL represents missing or unknown data. It is different from zero or an empty string, as NULL means that no value has been assigned. SQL provides functions like IS NULL and IS NOT NULL to handle NULL values in queries.

15. What is the difference between INNER JOIN and OUTER JOIN?

How to Answer:

• Explain INNER JOIN – it returns matching rows between two tables.
• Define OUTER JOIN – it returns all records, including unmatched rows.
• Break down the different types of OUTER JOIN (LEFT, RIGHT, FULL).

Sample Answer:

INNER JOIN returns only the matching rows from both tables based on a common column. OUTER JOIN returns all records from one or both tables, including unmatched rows. OUTER JOIN is further divided into LEFT JOIN, RIGHT JOIN, and FULL JOIN, each determining how unmatched rows are handled.

16. What is a subquery in SQL?

How to Answer:

• Describe a subquery as a query within another query.
• Explain its use to retrieve data for the main query.
• Mention where subqueries can be used (SELECT, WHERE, FROM).

Sample Answer:

A subquery is a query nested within another SQL query. It is used to retrieve data that will be used by the main query. Subqueries can be placed in SELECT, WHERE, or FROM clauses to filter or refine results dynamically.

17. What is the difference between GROUP BY and ORDER BY?

How to Answer:

• Define GROUP BY – used for grouping rows with aggregate functions.
• Define ORDER BY – used to sort results in ascending/descending order.
• Emphasize the difference: GROUP BY organizes data, ORDER BY sorts data.

Sample Answer:

• GROUP BY is used to group rows based on common values, often with aggregate functions like SUM or COUNT.
• ORDER BY is used to sort results in ascending or descending order based on one or more columns.
• GROUP BY groups data, while ORDER BY arranges it in a specified order.

18. What is a view in SQL?

How to Answer:

• Define a view as a virtual table.
• Explain that it does not store data but dynamically displays it from other tables.
• Mention that views improve security and simplify complex queries.

Sample Answer:

A view is a virtual table based on the result of a SQL query. It does not store data physically but displays data dynamically from existing tables. Views improve security by restricting direct table access and simplifying complex queries.

Also Read: SQL For Beginners: Essential Queries, Joins, Indexing & Optimization Tips

19. What are aggregate functions in SQL?

How to Answer:

• List common aggregate functions like SUM(), AVG(), COUNT(), MAX(), MIN().
• Explain their purpose: to perform calculations on sets of data.
• Provide examples of their typical use.

Sample Answer:

Aggregate functions perform calculations on a set of values and return a single result. Common aggregate functions include:

• SUM() – Calculates the total sum of a column.
• AVG() – Returns the average value.
• COUNT() – Counts the number of rows.
• MAX() / MIN() – Finds the highest and lowest values.

20. What is a self-join in SQL?

How to Answer:

• Define self-join – a join where a table is joined with itself.
• Explain the purpose of comparing rows within the same table.
• Mention the use of table aliases to differentiate between instances.

Sample Answer:

A self-join is a join where a table is joined with itself. It is used when comparing rows within the same table. A self-join requires using table aliases to differentiate between the original and duplicate instances of the table.

21. What is the difference between DELETE and TRUNCATE?

How to Answer:

• Define DELETE – it removes specific rows and can be rolled back.
• Define TRUNCATE – it removes all rows and cannot be rolled back.
• Compare performance: DELETE is slower, TRUNCATE is faster.

Sample Answer:

DELETE removes specific rows from a table based on a condition and can be rolled back. TRUNCATE removes all rows from a table without logging individual row deletions and cannot be rolled back. DELETE is slower as it logs changes, while TRUNCATE is faster as it resets the table structure.

22. What are the constraints in SQL?

How to Answer:

• List common constraints: PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK.
• Define each constraint and its purpose.
• Explain how constraints maintain data integrity in tables.

Sample Answer:

Constraints are rules applied to table columns to maintain data integrity. Common constraints include:

• PRIMARY KEY – Uniquely identifies records.
• FOREIGN KEY – Links two tables.
• UNIQUE – Ensures unique values in a column.
• NOT NULL – Prevents NULL values.
• CHECK – Enforces a condition on data.

These basic SQL interview questions set the stage by covering the essentials. Now, it’s time to level up. In the next section, we dive into intermediate SQL questions that challenge your grasp of more complex queries and real-world problem-solving.

Intermediate Level SQL Interview Questions and Answers

If you're at an intermediate level and preparing for an SQL interview, expect questions that focus on more complex topics, such as subqueries, advanced joins, and query optimization. These questions will test your ability to handle intricate data and improve query performance.

Let’s go through the key areas you need to understand.

23. What is a JOIN in SQL, and what are its types?

A JOIN is used to combine rows from multiple tables based on a related column. The main types are:

How to Answer:

• Define JOIN as a method to combine rows from multiple tables based on a related column.
• List the main types.

Sample Answer:

• INNER JOIN: Returns matching rows from both tables.
• LEFT JOIN: Returns all rows from the left table and matching rows from the right.
• RIGHT JOIN: Returns all rows from the right table and matching rows from the left.
• FULL JOIN: Returns all rows when there is a match in either table.

24. What is a subquery? Provide an example.

How to Answer:

• Define a subquery as a query inside another query.
• Mention its use to retrieve data for the main query.
• Provide an example query.

Sample Answer:

A subquery is a query within another SQL query that helps retrieve data dynamically. It can be used in SELECT, INSERT, UPDATE, or DELETE statements.
 Example:

SELECT name FROM employees  
WHERE department_id = (SELECT department_id FROM departments WHERE department_name = 'HR');

This returns employees who work in the HR department.

25. Explain the difference between UNION and UNION ALL.

How to Answer:

• Define UNION: Combines results and removes duplicates.
• Define UNION ALL: Combines results and retains duplicates.
• Explain that UNION is slower due to sorting and removing duplicates, while UNION ALL is faster.

Sample Answer:

• UNION combines results from multiple queries and removes duplicates, while
• UNION ALL keeps duplicates. UNION takes longer as it sorts and filters duplicates, whereas UNION ALL is faster but may return repeated values.

26. Explain ACID properties in SQL.

How to Answer:

Explain the properties of each element one by one. 

Sample Answer:

ACID properties ensure reliable database transactions:

• Atomicity: Transactions are fully completed or not executed at all.
• Consistency: Data remains valid before and after a transaction.
• Isolation: Transactions do not interfere with each other.
• Durability: Completed transactions are permanently saved.

27. What is the difference between DELETE, TRUNCATE, and DROP?

How to Answer:

Explain the difference between these three one by one. 

Sample Answer:

• DELETE: Removes specific rows and can be rolled back.
• TRUNCATE: Removes all rows but keeps the table structure; cannot be rolled back.
• DROP: Deletes the entire table, including its structure.

28. What is an index in SQL, and what are its types?

How to Answer:

• Define an index as a mechanism to speed up query performance.
• Clustered Index: Sorts and stores data physically in a specific order.
• Non-Clustered Index: Creates a separate structure pointing to data locations without affecting physical storage.

Sample Answer:

An index in SQL improves query performance by speeding up data retrieval.

• Clustered Index: Sorts and stores data physically in a specific order.
• Non-Clustered Index: Creates a separate structure pointing to data locations without affecting physical storage.

29. What are stored procedures in SQL?

How to Answer:

• Define stored procedures as precompiled SQL queries stored in the database.
• Mention that stored procedures improve performance and reduce network traffic.
• Highlight that stored procedures enhance security by limiting direct access to data.

Sample Answer:

A stored procedure is a precompiled SQL query stored in the database. It helps improve performance, reduce network traffic, and enhance security by limiting direct table access.

30. What is the difference between a view and a table?

How to Answer:

• A table stores data physically in the database.
• A view is a virtual table based on the result of an SQL query.
• Views simplify complex queries and provide an additional layer of security by restricting data access.

Sample Answer:

A table stores data physically, while a view is a virtual table based on an SQL query. Views simplify complex queries and enhance security by restricting data access.

31. What is normalization? Name its types.

How to Answer:

• Define normalization as the process of organizing data to reduce redundancy.
• Name the types.

Sample Answer:

Normalization reduces redundancy and improves data consistency. The main types are:

• 1NF: Eliminates duplicate columns and ensures atomicity.
• 2NF: Removes partial dependencies.
• 3NF: Eliminates transitive dependencies.

32. What is the difference between RANK(), DENSE_RANK(), and ROW_NUMBER()?

How to Answer:

Explain the difference between these three one by one. 

Sample Answer:

• RANK(): Assigns ranks but skips numbers for duplicate values.
• DENSE_RANK(): Assigns ranks without skipping numbers for duplicates.
• ROW_NUMBER(): Assigns a unique sequential number to each row.

33. What is a trigger in SQL?

How to Answer:

• Define a trigger as an automatic action executed when a specific event occurs (INSERT, UPDATE, DELETE).
• Explain that triggers help enforce business rules and maintain data consistency.

Sample Answer:

A trigger is an automatic database action executed when a specific event (INSERT, UPDATE, DELETE) occurs. It helps maintain data consistency by enforcing business rules.

34. What is a cursor in SQL?

How to Answer:

• Define a cursor as a tool for row-by-row processing of query results.
• Explain that cursors are useful for handling individual records, but are slower than set-based operations.

Sample Answer:

A cursor allows row-by-row processing of query results. It is useful for handling individual records but is slower compared to set-based operations.

35. What is the difference between HAVING and WHERE clauses?

How to Answer:

Explain the difference between these two clauses.

Sample Answer:

• WHERE: Filters records before aggregation and applies to individual rows.
• HAVING: Filters grouped records after aggregation using functions like SUM() or COUNT().

36. What is the difference between a candidate key and a primary key?

How to Answer:

Explain the difference between these two keys.

Sample Answer:

A candidate key is any column or set of columns that can uniquely identify a record. A primary key is a selected candidate key that uniquely identifies rows and cannot have NULL values.

37. What is the COALESCE function in SQL?

How to Answer:

• Define COALESCE() as a function that returns the first non-NULL value from a list.
• Provide an example.

Sample Answer:

The COALESCE() function returns the first non-null value from a list.

Example:

SELECT COALESCE(NULL, 'Data Science', 'SQL'); -- Output: 'Data Science'

It ensures NULL values are replaced with meaningful data.

Having covered the intermediate-level SQL interview questions, let us check some SQL interview questions suitable for experienced candidates. 

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SQL Interview Questions for Experienced

If you're an experienced professional preparing for an SQL interview, expect questions on advanced topics such as query optimization, complex joins, and database design. These questions will evaluate your ability to manage large datasets, fine-tune performance, and solve intricate database issues.

In this section, you'll find SQL interview questions for experienced candidates along with detailed answers to help you improve your skills. Let’s go over the key concepts you should be familiar with.

38. Explain different isolation levels in SQL.

How to Answer:

• Define isolation levels as ways to control how transactions interact with each other.
• List the main isolation levels.

Sample Answer:

Isolation levels define how transactions interact with each other to maintain data integrity. The four main isolation levels are:

• Read Uncommitted: Allows dirty reads, where uncommitted changes are visible.
• Read Committed: Prevents dirty reads but allows non-repeatable reads.
• Repeatable Read: Prevents dirty and non-repeatable reads but allows phantom reads.
• Serializable: The strictest level, preventing all concurrency issues by locking rows.

39. How does a clustered index work?

How to Answer:

• Define a clustered index as determining the physical order of data in a table.
• Explain that only one clustered index is allowed per table since data is stored in sorted order based on the indexed column.
• Highlight its advantage in improving search performance for range queries but note it can slow down insertions and updates.

Sample Answer:

A clustered index determines the physical order of data in a table. Each table can have only one clustered index, as the data is stored in sorted order based on the indexed column. It improves search performance for range queries but slows down insertions and updates.

40. What is a window function in SQL?

How to Answer:

• Define a window function as performing calculations over a set of rows related to the current row.
• Emphasize that window functions do not group results but retain individual row data.

Sample Answer:

A window function performs calculations across a set of table rows related to the current row. Unlike aggregate functions, it does not group results but retains individual row data. Examples include RANK(), DENSE_RANK(), ROW_NUMBER(), and SUM() OVER().

41. What is the difference between a CTE and a temporary table?

How to Answer:

• Define a CTE (Common Table Expression) as a temporary result set within a query, defined using the WITH clause.
• Explain that CTEs improve query readability and recursion handling.
• Define a temporary table as a table that exists temporarily in the database, lasting until it is manually dropped or the session ends.

Sample Answer:

A Common Table Expression (CTE) is a temporary result set within a query using the WITH clause. It improves readability and recursion handling. A temporary table is created in the database temporarily and persists until manually dropped or the session ends.

Also Read: Is SQL Hard to Learn? Breaking Down the Challenges and Solutions

42. What are materialized views in SQL?

How to Answer:

• Define materialized views as stored query results that are periodically refreshed.
• Explain that unlike regular views, which fetch real-time data, materialized views store data physically.
• Highlight that materialized views improve query performance for complex calculations.

Sample Answer:

A materialized view is a stored query result that is periodically refreshed. Unlike regular views, which fetch real-time data, materialized views store data physically, improving query performance for complex calculations.

43. What is the difference between NOLOCK and READ COMMITTED in SQL?

How to Answer:

Explain the difference between these two in brief.

Sample Answer:

• NOLOCK: Allows reading data without acquiring locks, leading to dirty reads.
• READ COMMITTED: Ensures only committed data is read, preventing dirty reads but allowing non-repeatable reads.

44. What is sharding in SQL databases?

Sharding is a database partitioning method where large datasets are split across multiple servers to improve performance and scalability. Each shard operates independently, reducing the load on a single database instance.

45. What is database normalization, and when should denormalization be used?

How to Answer:

• Define sharding as a method of database partitioning that splits large datasets across multiple servers.
• Explain that each shard operates independently, helping to improve performance and scalability.
• Highlight that sharding reduces the load on a single database instance.

Sample Answer:

Normalization organizes data efficiently to eliminate redundancy and improve consistency. Denormalization is used when performance is prioritized over redundancy, such as in reporting databases where fewer joins improve query speed.

46. Explain the difference between an OLTP and an OLAP system.

How to Answer:

• Define normalization as organizing data to eliminate redundancy and improve consistency.
• Explain that denormalization is used when performance is prioritized over redundancy. 

Sample Answer:

• OLTP (Online Transaction Processing): Handles real-time transactions, optimized for quick inserts and updates (e.g., banking systems).
• OLAP (Online Analytical Processing): Designed for complex queries and reporting, optimized for read-heavy operations (e.g., data warehouses).

47. How does indexing impact SQL performance?

How to Answer:

• Indexing speeds up data retrieval by creating a structure to find data faster.
• Mention that indexing slows down INSERT, UPDATE, and DELETE operations due to the need for additional maintenance.
• Emphasize the importance of selecting the appropriate index type (clustered, non-clustered, composite, unique) for optimization.

Sample Answer:

Indexing speeds up data retrieval but slows down inserts, updates, and deletes due to additional maintenance. Choosing the right index type (clustered, non-clustered, composite, or unique) is crucial for optimizing SQL performance.

48. What is the difference between EXISTS and IN operators?

How to Answer:

Explain the difference between these two in brief.

Sample Answer:

• EXISTS: Checks for the existence of records in a subquery and stops once a match is found, making it more efficient for large datasets.
• IN: Compares a value against a list of values and is better suited for small, predefined lists.

49. What is a deadlock in SQL, and how can it be prevented?

How to Answer:

• Define deadlock as a situation where two transactions hold resources that the other needs, preventing both from progressing.
• Explain ways to prevent deadlocks:
  • Ensure consistent transaction order.
  • Use shorter transactions.
  • Implement deadlock detection mechanisms.

Sample Answer:

A deadlock occurs when two transactions hold resources the other needs, preventing progress. It can be avoided by ensuring consistent transaction order, using shorter transactions, and implementing deadlock detection mechanisms.

50. What is partitioning in SQL, and what are its types?

How to Answer:

• Define partitioning as dividing large tables into smaller, more manageable pieces for better performance.
• List the types of partitioning.

Sample Answer:

Partitioning splits large tables into smaller, manageable pieces for better performance. Types include:

• Range Partitioning: Based on a value range (e.g., sales data by year).
• List Partitioning: Based on predefined list values (e.g., region-based partitions).
• Hash Partitioning: Uses a hash function for even distribution.

These SQL interview questions for experienced professionals will help you tackle high-level database challenges in MNC interviews.  In the next section, let's have a look at some actionable tips that can help you crack your SQL interview questions with ease. 

SQL Interview Preparation Tips

Preparing for an SQL interview requires a solid grasp of database concepts, problem-solving skills, and the ability to apply SQL in different scenarios. Whether you are a beginner or an experienced professional, these key strategies will help you tackle SQL interview questions with confidence. 

Let's go through the strategies that will help you succeed in your SQL interview.

• Understand the Basics Thoroughly

  Ensure a solid foundation in core basic SQL concepts by mastering key commands and queries.

  • Review essential SQL commands like SELECT, INSERT, UPDATE, and DELETE.
  • Practice simple queries, including filtering, sorting, and limiting results.
  • Write basic queries using INNER JOIN and LEFT JOIN for multiple tables.

• Practice Query Optimization

  Focus on improving query performance and efficiency during interviews.

  • Use EXPLAIN to analyze and optimize your queries.
  • Familiarize yourself with indexing and its impact on performance.
  • Avoid unnecessary subqueries when a JOIN can be more efficient.

• Master Different Join Types

  Be comfortable with all join types and understand when to use them.

  • Practice writing queries with INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
  • Learn to join multiple tables and apply appropriate filters.

Also Read: SQL Jobs for Freshers: Salary, Career Growth & Opportunities

• Understand Normalization and Data Integrity

  Know how to organize data and maintain consistency within your database.

  • Study the concepts of 1NF, 2NF, and 3NF.
  • Practice designing normalized databases with proper relationships and constraints like PRIMARY KEY and FOREIGN KEY.

• Work on Complex Queries and Subqueries

  Be prepared for questions involving nested queries and complex data retrieval.

  • Practice writing both correlated and non-correlated subqueries.
  • Example: Use a subquery to find employees from a department with more than 50 employees.

• Get Comfortable with Aggregation and Grouping

  Understand how to use aggregation functions and group data effectively.

  • Use GROUP BY with aggregate functions like SUM(), COUNT(), AVG(), MAX(), and MIN().
  • Practice filtering groups with HAVING.

• Prepare for Data Manipulation and Transactions

  Be ready for questions about modifying data and handling transactions.

  • Write queries for INSERT, UPDATE, and DELETE operations.
  • Understand how to use COMMIT, ROLLBACK, and SAVEPOINT to manage transactions.

Also Read: SQL Vs MySQL: Difference Between SQL and MySQL

• Know How to Handle NULL Values

  Learn how to manage NULL values in your queries.

  • Use IS NULL and IS NOT NULL for filtering NULL values.
  • Practice using COALESCE() to replace NULL values with meaningful data.

• Understand Indexing and Its Impact

  Know when to use indexes and their effect on query performance.

  • Understand the difference between CLUSTERED and NON-CLUSTERED indexes.
  • Practice creating indexes and analyzing their impact on query execution.

• Review SQL Server-Specific Features

  Familiarize yourself with the unique features of the specific RDBMS you’ll be using.

  • Learn specific SQL Server features like CROSS APPLY and FOR XML PATH.
  • If using MySQL or PostgreSQL, understand their distinct functionalities.

• Test Your Knowledge with Mock Interviews

  Practice answering SQL questions under interview conditions.

  • Use mock interview platforms or study with a peer.
  • Time yourself to improve your ability to respond quickly and confidently.

By following these SQL interview preparation tips, you can improve your confidence and problem-solving abilities, making you well-prepared to handle both basic and advanced SQL interview questions.

How upGrad Can Help You in Your SQL Career? 

By now, you’ve familiarized yourself with the key SQL interview questions that are critical for success in 2025. You’ve learned what employers are looking for, from query optimization to database design and handling complex data. With this knowledge in hand, you’re now equipped to approach your SQL interview with confidence and clarity. 

If you're looking to build on your SQL skills, upGrad’s courses offer practical learning and expert guidance. These programs are designed to help you close skill gaps and advance in your career. 

Here are some additional courses to get you started: 

• Executive Programme in Generative AI for Leaders
• Advanced Generative AI Certification Course
• Data Structures & Algorithms
• Professional Certificate Program in Cloud Computing and DevOps

Feeling unsure about where to begin your career in SQL? Connect with upGrad’s expert counselors or visit your nearest upGrad offline centre to explore a learning plan tailored to your goals. 

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