Top 50 SQL Server Interview Questions and Answers to Get Hired

Edited By Team Careers360 | Updated on Apr 17, 2024 03:03 PM IST | #SQL

In today's data-driven world, the role of data in shaping business decisions is undeniable. This significance has propelled the need for efficient database management systems (DBMS) like Microsoft SQL Server. This article explores Microsoft SQL Server interview questions and answers, providing insights for both freshers as well as experienced professionals. If you are looking to become a Data Administrator then this article is for you.

Top 50 SQL Server Interview Questions and Answers to Get Hired

These SQL server interview questions and answers directed towards freshers are designed for beginners to help them better understand and revise their concepts before appearing for their interview.

Q1. What is a database management system (DBMS)?

This is one of the important SQL Server Interview Questions that can be asked to test your understanding. A database management system (DBMS) is software that helps manage and organise data in a structured way, making it easier to store, retrieve, and manipulate information.

Q2. Explain the difference between a relational database and a non-relational database.

This is another one of the must know SQL server interview questions and answers for freshers. A relational database stores data in tables with predefined relationships, while a non-relational database stores data in more flexible formats like documents or key-value pairs.

Q3. What is SQL, and how is it used in databases?

This is amongst the top SQL server interview questions for freshers. SQL (Structured Query Language) is a language used to communicate with databases. It helps you perform tasks like querying data, updating records, and defining structures.

Q4. Can you explain primary keys and foreign keys in a database?

A primary key uniquely identifies a record in a table, while a foreign key establishes a link between two tables based on related data. These SQL server interview questions for freshers can be asked by the interviewer to check your knowledge.

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Q5. How does normalisation help in database design?

This is the topic that must be included in your SQL server interview questions and answers preparation list. Normalisation plays a crucial role in database design by systematically structuring data to minimise redundancy and enhance data integrity. By organising information into distinct tables according to their inherent relationships, normalisation eliminates unnecessary duplication of data, leading to a more efficient and streamlined database. This process not only conserves storage space but also prevents inconsistencies and anomalies that may arise from redundant information.

As a result, database systems that undergo normalisation are better equipped to handle complex queries, maintain accurate records, and facilitate smoother operations within a given application or system.

Q6. Explain the concept of ACID properties in database transactions.

This is another one of the top

. ACID stands for Atomicity, Consistency, Isolation, and Durability. It ensures that database transactions are reliable and maintains data integrity.

Q7. What is a stored procedure in SQL, and why is it useful?

This is amongst the top SQL server interview questions and answers you should practice for better preparation. A stored procedure is a pre-written set of SQL statements that can be executed together. It is useful for reducing redundancy, enhancing security, and improving performance.

Q8. What is a database schema?

A database schema defines the structure and organisation of a database, including tables, columns, relationships, and constraints. An interviewer can ask you this type of SQL server interview questions and answers apt for freshers.

Q9. Explain the difference between a primary key and a unique key.

A primary key and a unique key are both crucial concepts in database management, distinguished primarily by their handling of null values. A primary key serves as a unique identifier for a record within a table, ensuring each entry is distinct and cannot be left empty. This attribute is fundamental for maintaining data integrity and facilitating efficient data retrieval.

On the other hand, a unique key also guarantees uniqueness among records but allows for the possibility of containing null values. While this distinction grants some flexibility in unique key usage, it is important to note that null values within a unique key should be used judiciously, as they can potentially complicate data handling and querying processes.

Q10. What is normalisation, and why is it important?

This is amongst the important SQL server interview questions and answers you must prepare for. Normalisation, a pivotal concept in database management, encompasses the systematic structuring of data to eradicate redundancy and bolster data integrity. By minimising duplication and ensuring each piece of information is stored in a single location, normalisation curtails the likelihood of inconsistencies or errors within the dataset. This meticulous process is indispensable in upholding the accuracy and reliability of databases, guaranteeing that information remains reliable and coherent, ultimately enhancing the efficiency of data retrieval and manipulation operations.

Q11. What is a SQL JOIN, and how does it work?

A SQL JOIN is a crucial topic that you must practice while preparing for SQL server interview questions and answers. It is an essential operation in database management that facilitates the amalgamation of data from two or more tables by leveraging a shared column. This enables the user to extract comprehensive information from diverse sources within a database. By employing JOINs, users can establish relationships between different sets of data, making it possible to retrieve correlated information in a single, coherent dataset.

This process not only enhances the efficiency of data retrieval but also empowers database administrators and analysts to draw valuable insights from the interconnected information stored across various tables.

Q12. Explain the concept of data integrity in a database.

This is one of the top SQL server interview questions for freshers. Data integrity ensures that data is accurate, consistent, and reliable. It involves maintaining the correctness of data throughout its lifecycle.

Q13. What is a database index, and why is it useful?

A database index is a data structure that improves query performance by allowing faster data retrieval. It works like an organised reference system. This is one of the must-know SQL server interview questions for freshers to prepare for a better performance.

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Q14. What is a transaction in a database, and why is it important?

This is one of the essential SQL server interview questions for freshers that can be asked to check your knowledge. A transaction is a sequence of database operations treated as a single unit. It ensures data consistency and prevents data corruption.

Q15. What are database constraints, and why are they used?

Database constraints define rules that data must follow to maintain data integrity. They ensure data accuracy and prevent unwanted changes.

Q16. What is the difference between a WHERE clause and a HAVING clause in SQL?

The WHERE clause filters rows before they are grouped, while the HAVING clause filters grouped rows after aggregation. You must know these interview questions for better preparation.

Q17. What is the purpose of the GROUP BY clause in SQL?

The GROUP BY clause in SQL serves a crucial role in data analysis and reporting. By employing this clause, one can categorise rows with identical values in designated columns, subsequently enabling the application of aggregate functions like SUM, AVG, COUNT, and more. This facilitates the consolidation of data into meaningful summaries, offering valuable insights into trends, patterns, and overall statistics within a dataset. Essentially, GROUP BY empowers users to distill complex information into manageable, actionable conclusions, making it an indispensable tool for extracting meaningful intelligence from large datasets.

Q18. Explain the concept of a self-join in SQL.

A self-join in SQL involves the process of connecting a table with itself, essentially treating it as two separate entities within the same query. This technique is valuable when there exists a logical relationship between different rows of the same table, typically identified by a shared column or attribute. By employing self-joins, one can compare and retrieve information from these related rows in a structured and meaningful way, facilitating tasks such as hierarchical data representation or analysing connections within a single dataset.

This approach proves particularly useful in scenarios where self-referential relationships, like organisational hierarchies or network graphs, need to be explored and manipulated for data analysis or reporting purposes.

Q19. What is a subquery in SQL, and how is it used?

A subquery is a query nested within another query. It is used to retrieve data needed for the main query or to perform calculations.

Q20. What is the purpose of the UNION operator in SQL?

This is one of the frequently asked SQL server interview questions and answers. The UNION operator combines the result sets of two or more SELECT statements, removing duplicates by default.

Q21. Explain the difference between a view and a table in SQL.

This type of SQL server interview questions and answers is frequently asked in interviews. A table stores data physically, while a view is a virtual table that displays data from one or more tables based on specified criteria.

Q22. What is a correlated subquery, and when might you use it?

This is amongst the must know SQL server interview questions and answers. A correlated subquery refers to an inner query that depends on values from the outer query. It is used when filtering based on related data from the outer query.

Q23. How can you prevent SQL injection attacks in your queries?

To prevent SQL injection, use parameterised queries, prepared statements, or stored procedures to ensure user input is treated as data, not code.

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Q24. Explain the purpose of the RANK() function in SQL.

The RANK() function in SQL serves the purpose of providing a distinctive rank to each row within a given result set based on specified criteria. This function is particularly valuable in scenarios where you need to establish a hierarchical order among rows, such as in competitions or rankings. It allocates a unique numerical rank to each row, ensuring that no two rows share the same rank.

However, in cases where multiple rows possess identical values that determine their ranking, the RANK() function may introduce gaps in rank values to accommodate these tied rows, ensuring the subsequent rank is appropriately adjusted. This feature proves invaluable in accurately representing the relative positions of data points within a dataset, facilitating effective analysis and decision-making.

Q25. What is the purpose of the COALESCE() function in SQL?

The COALESCE() function returns the first non-null value among its arguments, providing a way to handle null values effectively. This is one of the most essential SQL server interview questions for freshers.

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This one of those interview questions and answers will help professionals brush up on their concepts and prepare confidently for their interviews. Let us dive into the SQL server interview questions and answers for experienced professionals.

Q26. Differentiate between clustered and non-clustered indexes in SQL.

A clustered index determines the physical order of data in a table, while a non-clustered index creates a separate structure that points to the data.

Q27. Explain the concept of deadlock in a database system.

In a database system, a deadlock is a critical impasse that arises when two or more transactions find themselves in a stalemate, with each holding a resource that the other needs to progress. This results in a standstill, as neither transaction can proceed without the release of the coveted resource by the other. Picture it as a digital traffic jam, where multiple cars are at an intersection, but none can move forward because they are all waiting for another vehicle to yield.

This scenario can paralyse a database, causing a halt in operations until the deadlock is resolved through intervention mechanisms like timeouts, resource preemption, or transaction rollback. It is a crucial challenge to address in database management to ensure smooth and efficient system performance. This is amongst the SQL server interview questions and answers for experienced professionals as well as freshers.

Q28. What is an execution plan in SQL, and why is it important?

This is one of the essential SQL server interview questions and answers for experienced professionals. An execution plan is a set of steps that the database engine follows to execute a query. It is crucial for optimising query performance.

Q29. Can you elaborate on the CAP theorem in distributed databases?

The CAP theorem, also known as Brewer's theorem, is a fundamental principle in distributed databases. It asserts that in a distributed system, it is impossible to achieve all three crucial properties: Consistency (all nodes have the same data at the same time), Availability (a guarantee that every request receives a response, even if it is a failure message), and Partition tolerance (the system continues to operate despite network partitions). Instead, a distributed system can only guarantee two of these properties at any given time, which leads to crucial design decisions in distributed database architectures. This theorem serves as a guiding principle for architects and engineers when making trade-offs in system design.

Q30. What are NoSQL databases, and when should you consider using them?

NoSQL databases are non-relational databases that offer flexibility, scalability, and high performance. They are great for handling large volumes of unstructured data. This type of SQL server interview questions and answers for experienced can be asked to check your understanding.

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Q31. Explain the concept of data warehousing and its benefits.

Data warehousing is a comprehensive approach to gather, store, and oversee data from diverse origins with the aim of facilitating thorough analysis. This system offers a unified perspective, enabling astute decision-making by presenting a cohesive and organised pool of information. Essentially, it acts as a centralised reservoir that not only ensures data integrity but also empowers businesses with the insights they need to make informed choices, ultimately driving efficiency and effectiveness in their operations.

Q32. What is query optimisation, and how can it improve database performance?

You should give priority to these SQL server interview questions and answers for experienced ones to strengthen your preparation. Query optimisation involves fine-tuning SQL queries to make them run faster and use resources efficiently. It enhances overall database performance.

Q33. How does sharding work in database scaling?

Sharding involves splitting a large database into smaller, manageable pieces called shards. Each shard is stored on a separate server, improving scalability.

Q34. Explain the concept of in-memory databases.

In-memory databases store data in the system's main memory rather than on disk. This leads to faster data retrieval and processing.

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Q35. How does columnar storage differ from row-based storage in databases?

In columnar storage, data is stored in columns rather than rows, which can lead to better compression and faster analytical queries. You should focus more on these SQL server interview questions and answers for experienced ones to strengthen your preparation.

Q36. Can you discuss the trade-offs between using GUIDs and integers as primary keys?

GUIDs (Globally Unique Identifiers) offer universality but can lead to fragmentation and larger storage. Integers are like using roll numbers – efficient but may run out eventually. It is a balance between distinctiveness and practicality.

Q37. Explain the concept of materialised views in databases.

Materialised views in databases are essentially pre-calculated outcomes of SQL queries that are stored as tables. These views serve to bolster query efficiency by circumventing the need for redundant computations. Instead of recalculating results every time a query is made, materialised views store the precomputed data, significantly reducing the processing time required for subsequent queries. This not only optimises performance but also proves invaluable in scenarios where complex or resource-intensive queries are involved, leading to a more streamlined and responsive database system.

Q38. Can you describe the differences between OLAP and OLTP databases?

OLAP (Online Analytical Processing) databases are used for complex queries and reporting, while OLTP (Online Transaction Processing) databases handle day-to-day operations.

Q39. What is database denormalisation, and when is it suitable?

Database denormalisation involves intentionally introducing redundancy to improve query performance. It is suitable for read-heavy applications. Prepare these SQL server interview questions and answers for experienced ones to improve your preparation.

Q40. Can you explain the concept of database replication and its types?

Database replication is the process of duplicating a database onto multiple servers, allowing for increased availability, fault tolerance, and scalability. This ensures that data remains consistent across all copies, enhancing system resilience. There are different types of replication, with master-slave replication involving a primary server (master) that processes write operations and propagates changes to secondary servers (slaves). On the other hand, peer-to-peer replication enables multiple servers to act as both sources and recipients of data, facilitating a more distributed and balanced approach to handling database operations. Each type of replication serves distinct purposes, catering to various organisational needs for data management and accessibility.

Q41. What is the purpose of the NOLOCK hint in SQL Server?

This is one of the top SQL server interview questions and answers for experienced developers. The NOLOCK hint allows a query to read data from tables without acquiring locks, increasing query performance but potentially returning uncommitted data.

Q42. Explain the differences between a clustered index and a non-clustered index in SQL Server.

A clustered index in SQL Server organises the actual data within a table based on the indexed column(s), physically arranging it for efficient retrieval. This means the rows are stored in the order of the clustered index key, making it faster to retrieve specific ranges of data. On the other hand, a non-clustered index creates a separate structure that contains pointers to the actual data rows. This allows for quick access to specific records without altering the physical order of the table, making it useful for scenarios where you frequently need to search for specific values but do not want to reorganise the underlying data.

Q43. What is the purpose of the OUTPUT clause in SQL Server?

The OUTPUT clause allows you to capture the results of modifications (inserts, updates, deletes) and use them in subsequent operations.

Q44. Explain the concept of table-valued functions in SQL Server.

Table-valued functions in SQL Server are custom functions created by users that yield a table as their output. They function much like regular tables in queries, offering a dynamic and versatile way to retrieve and manipulate data. This capability proves invaluable in scenarios where complex data operations are required, allowing for efficient and modular code design in SQL.

Q45. How does the TRY...CATCH block work in SQL Server error handling?

The TRY...CATCH block allows you to handle errors gracefully by enclosing potentially error-prone code in the TRY section and providing error-handling logic in the CATCH section.

Q46. What is the purpose of the PIVOT and UNPIVOT operators in SQL Server?

The PIVOT operator transforms rows into columns, while the UNPIVOT operator does the opposite, converting columns to rows. You must practice these kinds of SQL server interview questions and answers for experienced professionals.

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Q47. Explain the concept of database snapshots in SQL Server.

Database snapshots in SQL Server offer a crucial functionality by allowing users to obtain a fixed, unchangeable snapshot of a database at a precise moment in time. These snapshots serve as read-only copies, invaluable for tasks like generating reports or retrieving data in case of unforeseen issues, offering a reliable safeguard for crucial information. This feature ensures that even as the database undergoes changes, this frozen snapshot remains unaffected, ensuring data integrity and enabling businesses to make informed decisions based on a consistent, reliable dataset.

Q48. What is the purpose of the FILESTREAM storage option in SQL Server?

This is another one of the must know SQL server interview questions and answers. The FILESTREAM storage option allows binary data (such as images or documents) to be stored as files on the file system while still being integrated with the database.

Q49. How does the MERGE statement work in SQL Server?

The MERGE statement in SQL Server is a powerful tool that combines multiple operations into one, streamlining data management. It essentially allows you to synchronise information between a source and target table by performing inserts, updates, and deletes in a single query. This means you can efficiently add new data, update existing records, and even remove outdated information, all in one go. This makes MERGE particularly useful for tasks like data warehousing, where maintaining consistent and up-to-date information is crucial for effective analysis and reporting. This is an important SQL server interview questions and answers to learn while sitting for an interview.

Q50. Explain the concept of temporal tables in SQL Server.

Temporal tables maintain historical versions of data, allowing you to query data as it appeared at specific points in time. This is one of the must-know SQL server interview questions and answers for experienced ones.

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Conclusion

This compilation of SQL server interview questions and answers provides a holistic view, from foundational concepts for freshers to advanced insights for professionals. By delving into topics like authentication modes, normalisation, and transactional behaviour, you are better prepared to demonstrate your expertise in SQL Server interviews. Thoroughly prepare these to excel in your SQL Server interviews with confidence and competence.

Frequently Asked Questions (FAQs)

1. What is the importance of SQL Server interview preparation?

Preparing for SQL Server interview questions and answers is crucial to showcase your expertise in database management. It demonstrates your ability to handle data effectively and make informed decisions, making you a valuable asset to potential employers.

2. How can I improve my SQL querying skills for interviews?

Practice writing SQL queries that retrieve, update, and manipulate data. Use online platforms and sample databases to work on real-world scenarios. This hands-on practice enhances your confidence and skills.

3. How should I approach behavioural questions during SQL Server interviews?

Be ready to discuss your experiences with SQL projects or challenges you have overcome. Highlight teamwork, problem-solving, and effective communication skills.

4. How can I stand out during a technical SQL Server interview?

Explain your thought process clearly while solving SQL problems. Focus on logical reasoning and optimisation strategies. Use the whiteboard to illustrate your solutions if necessary.

5. How should I approach a SQL Server coding test during an interview?

Read the problem statement carefully, design your query logically, and break it down into smaller steps. Test your code on sample data before submitting it.