Azure SQL Database Interview Questions and Answers for freshers

1. What is Azure SQL Database?

   • Answer: Azure SQL Database is a fully managed relational database service in the cloud, based on Microsoft's SQL Server engine. It offers scalability, high availability, and security without the need for managing the underlying infrastructure.

2. What are the different service tiers in Azure SQL Database?

   • Answer: Azure SQL Database offers several service tiers, including Basic, Standard, General Purpose, Business Critical, and Hyperscale. Each tier provides different levels of performance, scalability, and availability, catering to various workloads and budgets.

3. Explain the difference between General Purpose and Business Critical service tiers.

   • Answer: General Purpose offers a balance of compute and storage, suitable for various workloads. Business Critical provides higher availability (99.99%), higher performance, and better scalability, ideal for mission-critical applications.

4. What is DTU (Database Transaction Units)?

   • Answer: DTUs are a measurement unit that represents the compute power, storage, and I/O capacity of an Azure SQL Database. Choosing a DTU-based service tier involves selecting a predefined bundle of resources.

5. What is vCore?

   • Answer: vCores are virtual cores that represent the compute capacity in Azure SQL Database. Using a vCore-based purchasing model allows for more granular control over resources, enabling customization of compute, memory, and storage independently.

6. Explain the concept of elastic pools.

   • Answer: Elastic pools allow you to group multiple databases together and share a pool of resources. This is cost-effective for managing multiple smaller databases, as resources are shared among them based on demand.

7. What is Azure SQL Database Managed Instance?

   • Answer: Azure SQL Database Managed Instance is a service that offers a near 100% compatibility with on-premises SQL Server instances. It's ideal for migrating on-premises databases to Azure with minimal code changes.

8. How does Azure SQL Database ensure high availability?

   • Answer: Azure SQL Database uses features like automatic failover, read replicas, and geographically redundant deployments to ensure high availability and minimize downtime.

9. Explain the concept of read replicas in Azure SQL Database.

   • Answer: Read replicas are secondary databases that can handle read-only workloads, offloading the primary database and improving performance. They can be geographically distributed for disaster recovery and low-latency access from different regions.

10. What are some security features of Azure SQL Database?

    • Answer: Azure SQL Database offers various security features, including Azure Active Directory integration, encryption (at rest and in transit), row-level security, and threat detection.

11. How can you monitor the performance of your Azure SQL Database?

    • Answer: You can monitor performance using Azure portal, Azure Monitor, and SQL Server Management Studio (SSMS). These tools provide metrics on CPU, memory, I/O, and other key performance indicators.

12. What is Azure SQL Database Backup and Restore?

    • Answer: Azure SQL Database provides automatic backups by default. You can also manually back up and restore databases using the Azure portal, PowerShell, or T-SQL. Point-in-time restore allows recovery to a specific point in time.

13. What is Azure Data Studio?

    • Answer: Azure Data Studio is a free, cross-platform database tool that can be used to manage Azure SQL Database, along with other SQL Server instances.

14. What is a connection string? How is it used with Azure SQL Database?

    • Answer: A connection string contains the parameters required to connect to a database. In Azure SQL Database, it includes information like server name, database name, user ID, password, and encryption settings. It's used by applications to establish a connection.

15. Explain the concept of failover groups in Azure SQL Database.

    • Answer: Failover groups provide high availability and disaster recovery capabilities. They allow you to create a secondary database in a different region that can take over if the primary database fails.

16. What are some common performance tuning techniques for Azure SQL Database?

    • Answer: Techniques include creating indexes, optimizing queries, using appropriate data types, ensuring proper database design, and leveraging features like query caching and read replicas.

17. How do you handle database scaling in Azure SQL Database?

    • Answer: Scaling can be vertical (increasing resources within the same tier) or horizontal (using elastic pools or adding more databases). The method depends on the specific needs and the service tier used.

18. What are some common challenges faced when migrating to Azure SQL Database?

    • Answer: Challenges include compatibility issues, data migration complexities, schema changes, performance optimization, and security configuration.

19. How can you ensure data security in Azure SQL Database?

    • Answer: Implementing strong passwords, using Azure Active Directory authentication, enabling encryption, regularly patching the database, and using features like row-level security and threat detection are crucial.

20. What is Transparent Data Encryption (TDE)?

    • Answer: TDE encrypts the data files at rest in Azure SQL Database, protecting the data even if the storage is compromised.

21. What is Always On Availability Groups? How does it relate to Azure SQL Database?

    • Answer: Always On Availability Groups provide high availability and disaster recovery for SQL Server. While similar concepts exist in Azure SQL Database (like failover groups), Always On is primarily for on-premises or SQL Server VMs in Azure, not directly for Azure SQL Database's managed service.

22. What is a stored procedure? How is it used in Azure SQL Database?

    • Answer: A stored procedure is a pre-compiled SQL code block that can be executed repeatedly. In Azure SQL Database, it improves performance and code reusability, helping in managing database tasks more efficiently.

23. Explain the difference between a function and a stored procedure.

    • Answer: Functions return a value and are typically used within SQL statements, while stored procedures perform a series of actions and don't necessarily return a value. Stored procedures can be more complex and perform DML operations.

24. What is indexing in Azure SQL Database and why is it important?

    • Answer: Indexing creates data structures that speed up data retrieval. It's important for improving query performance, especially for large tables, by allowing the database to quickly locate specific rows.

25. What are different types of indexes in Azure SQL Database?

    • Answer: Common types include clustered indexes (one per table, defines the physical order), non-clustered indexes (multiple allowed, points to data rows), and unique indexes (ensure unique values).

26. What are triggers in Azure SQL Database and how are they used?

    • Answer: Triggers are special stored procedures automatically executed in response to specific events (like INSERT, UPDATE, DELETE) on a table. They're used for enforcing business rules, auditing data changes, and maintaining data integrity.

27. What is a view in Azure SQL Database?

    • Answer: A view is a stored query that acts as a virtual table. It simplifies complex queries and provides a customized view of data from one or more underlying tables, without actually storing the data separately.

28. What is the purpose of using transactions in Azure SQL Database?

    • Answer: Transactions ensure data consistency and atomicity. A transaction is a sequence of operations treated as a single unit of work. If any part fails, the entire transaction is rolled back.

29. Explain ACID properties of transactions.

    • Answer: ACID stands for Atomicity (all or nothing), Consistency (maintains data integrity), Isolation (transactions are independent), and Durability (changes persist even after failures).

30. What is a deadlock in Azure SQL Database? How can you prevent it?

    • Answer: A deadlock occurs when two or more transactions are blocked indefinitely, waiting for each other to release resources. Preventing deadlocks involves careful design, short transactions, and consistent locking strategies.

31. What are some common data types used in Azure SQL Database?

    • Answer: Common data types include INT, BIGINT, VARCHAR, NVARCHAR, CHAR, NCHAR, DATETIME, DATE, BIT, FLOAT, DECIMAL.

32. What is the difference between VARCHAR and NVARCHAR?

    • Answer: VARCHAR stores variable-length strings of characters, while NVARCHAR stores variable-length strings of Unicode characters, supporting a broader range of characters.

33. Explain JOIN operations in SQL.

    • Answer: JOIN operations combine rows from two or more tables based on a related column. Types include INNER JOIN (returns only matching rows), LEFT JOIN (returns all rows from the left table and matching rows from the right), RIGHT JOIN, and FULL OUTER JOIN.

34. What is a subquery? Provide an example.

    • Answer: A subquery is a query nested inside another query. Example: `SELECT * FROM Employees WHERE salary > (SELECT AVG(salary) FROM Employees);` This finds employees with salaries above the average.

35. What are aggregate functions in SQL? Give examples.

    • Answer: Aggregate functions perform calculations on a set of values and return a single value. Examples include COUNT, SUM, AVG, MIN, MAX.

36. Explain the use of GROUP BY and HAVING clauses.

    • Answer: GROUP BY groups rows with the same values in specified columns. HAVING filters grouped rows based on a condition, similar to WHERE but applied after grouping.

37. What are common SQL clauses used for data manipulation?

    • Answer: SELECT, FROM, WHERE, INSERT, UPDATE, DELETE.

38. Explain the importance of normalization in database design.

    • Answer: Normalization reduces data redundancy and improves data integrity by organizing data efficiently into tables. It minimizes data anomalies that can occur during INSERT, UPDATE, and DELETE operations.

39. What are the different normal forms (e.g., 1NF, 2NF, 3NF)?

    • Answer: First Normal Form (1NF) eliminates repeating groups of data, Second Normal Form (2NF) eliminates redundant data that depends on only part of the primary key, and Third Normal Form (3NF) eliminates transitive dependency.

40. What is an ER diagram? Why is it useful in database design?

    • Answer: An ER diagram (Entity-Relationship diagram) is a visual representation of entities (tables) and their relationships in a database. It's crucial for planning and designing a database efficiently.

41. What is a primary key and a foreign key?

    • Answer: A primary key uniquely identifies each row in a table. A foreign key establishes a link between two tables, referencing the primary key of another table, enforcing referential integrity.

42. What are constraints in SQL? Give some examples.

    • Answer: Constraints enforce rules on data. Examples include primary key constraints, foreign key constraints, unique constraints, NOT NULL constraints, CHECK constraints.

43. What are indexes in SQL and how do they affect query performance?

    • Answer: Indexes are data structures that improve the speed of data retrieval. They create a sorted lookup table for faster searching of rows, reducing the need for full table scans.

44. Explain different types of joins in SQL (INNER, LEFT, RIGHT, FULL OUTER).

    • 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 is the opposite of LEFT JOIN. FULL OUTER JOIN returns all rows from both tables.

45. What is the difference between clustered and non-clustered indexes?

    • Answer: A clustered index defines the physical order of data rows in a table. A non-clustered index is a separate structure that points to data rows, allowing multiple non-clustered indexes per table.

46. How do you handle NULL values in SQL queries?

    • Answer: Use IS NULL or IS NOT NULL in WHERE clauses to check for NULL values. Avoid using = or != with NULL values.

47. Explain the concept of a transaction in SQL and its importance.

    • Answer: A transaction is a sequence of operations treated as a single unit of work. Its importance lies in maintaining data consistency and integrity. If any part fails, the entire transaction is rolled back.

48. What are different isolation levels in SQL Server?

    • Answer: Isolation levels control how transactions interact with each other, preventing issues like dirty reads, non-repeatable reads, and phantom reads. Levels include Read Uncommitted, Read Committed, Repeatable Read, and Serializable.

49. What is a stored procedure? What are its benefits?

    • Answer: A stored procedure is a pre-compiled SQL code block. Benefits include improved performance, code reusability, better security, and easier maintenance.

50. What is a trigger in SQL? How does it differ from a stored procedure?

    • Answer: A trigger is automatically executed in response to specific events on a table (INSERT, UPDATE, DELETE). Unlike stored procedures, triggers are not explicitly called; they are event-driven.

51. Explain the concept of views in SQL. What are their advantages?

    • Answer: A view is a stored query that acts as a virtual table. Advantages include simplifying complex queries, providing customized views of data, and enhancing security by restricting access to underlying tables.

52. How do you handle errors in SQL stored procedures?

    • Answer: Use TRY...CATCH blocks to handle exceptions and gracefully manage errors. Log errors for debugging and monitoring.

53. What are common SQL functions for string manipulation?

    • Answer: Functions like SUBSTRING, REPLACE, CONCAT, LEN, UPPER, LOWER are frequently used for string manipulation.

54. What are common SQL functions for date and time manipulation?

    • Answer: Functions like GETDATE(), DATEADD(), DATEDIFF(), DAY(), MONTH(), YEAR() are used for date and time manipulation.

55. Explain the concept of database normalization and its importance.

    • Answer: Normalization organizes data to reduce redundancy and improve data integrity. It helps avoid data anomalies during data modification operations.

56. What are the different levels of database normalization (1NF, 2NF, 3NF)?

    • Answer: 1NF removes repeating groups, 2NF removes redundant data dependent on only part of the primary key, 3NF removes transitive dependencies.

57. What is an ER diagram and how is it used in database design?

    • Answer: An ER diagram visually represents entities (tables) and relationships. It's a blueprint for database design.

58. What is a self-join in SQL? Give an example.

    • Answer: A self-join joins a table to itself, useful for comparing rows within the same table. Example: Finding employees who report to each other.

59. How do you optimize SQL queries for performance?

    • Answer: Techniques include creating appropriate indexes, optimizing query structure, using efficient data types, and avoiding unnecessary operations.

60. What are common performance bottlenecks in SQL databases?

    • Answer: Bottlenecks can include slow queries, lack of indexes, insufficient resources (CPU, memory, I/O), poor database design, and inefficient application code.

61. How do you troubleshoot performance issues in a SQL database?

    • Answer: Use query execution plans, performance monitoring tools, logging, and profiling to identify slow queries and resource bottlenecks.

62. What are some best practices for database security?

    • Answer: Best practices include strong passwords, least privilege principle, encryption (TDE), regular patching, auditing, and using firewall rules.

63. How do you manage backups and restores in Azure SQL Database?

    • Answer: Azure SQL Database provides automated backups. You can also use tools to manage backups, restore to a point-in-time, and create backups for disaster recovery.

64. What is Azure SQL Database's pricing model?

    • Answer: Pricing is based on service tier (DTU or vCore based), compute resources, storage, and other features. There are different pricing models for various tiers and options.

65. How would you approach migrating an on-premises SQL Server database to Azure SQL Database?

    • Answer: Assess compatibility, choose migration method (e.g., using Azure Database Migration Service), test migration in a non-production environment, and plan for downtime and data synchronization.

66. What are some tools used for managing Azure SQL Database?

    • Answer: Azure portal, SQL Server Management Studio (SSMS), Azure Data Studio, PowerShell, and Azure CLI are common tools.

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