Microsoft SQL Server DBA Interview Questions Answers

1. What are the main features introduced in SQL Server 2022?

SQL Server 2022 introduces several new features, including Azure Synapse Link integration, Ledger for SQL Server, containing Availability Groups, enhanced Query Store, and improvements in security, performance, and availability.

2. Explain the difference between clustered and non-clustered indexes in SQL Server.

A clustered index sorts and stores the data rows in the table or view based on the key values. Each table can have only one clustered index. A non-clustered index, on the other hand, does not alter the way data is stored but creates a separate object within the table that points back to the original row, allowing for more than one non-clustered index per table.

3. What is a SQL Server Agent?

SQL Server Agent is a Microsoft Windows service that executes scheduled administrative tasks, which are called jobs in SQL Server. It can manage job scheduling, alert system, and operators for notifying event responses.

4. Can you explain what a transaction is in SQL Server?

A transaction in SQL Server is a single unit of work. If a transaction is successful, all of the data modifications made during the transaction are committed and become a permanent part of the database. If a transaction encounters errors and must be canceled or rolled back, then all of the data modifications are erased.

5. What are the ACID properties?

ACID stands for Atomicity, Consistency, Isolation, and Durability. These properties ensure that transactions are processed reliably: Atomicity guarantees that all operations within the work unit are completed successfully; Consistency ensures that the database properly changes states upon a successfully committed transaction; Isolation ensures that transactions are securely and independently processed simultaneously without interference; Durability guarantees that once a transaction is committed, it will remain so, even in the event of a power loss, crash, or error.

6. What is SQL Server Management Studio (SSMS)?

SQL Server Management Studio (SSMS) is an integrated environment for managing any SQL infrastructure, from SQL Server to Azure SQL Database. SSMS provides tools to configure, monitor, and administer instances of SQL, as well as to deploy, monitor, and upgrade the data-tier components used by your applications, and build queries and scripts.

7. How do you back up a SQL Server database?

To back up a SQL Server database, you can use the BACKUP DATABASE command, specifying the name of the database to back up and the location to store the backup file.

8. What is a SQL Server trigger?

A trigger in SQL Server is a special kind of stored procedure that automatically runs when certain events occur in the database table, such as insert, update, or delete operations.

9. Can you explain what a deadlock is and how SQL Server handles deadlocks?

A deadlock occurs when two or more sessions are waiting for each other to release locks, in a circular chain, so that they can proceed with their transaction. SQL Server detects deadlocks automatically and resolves them by choosing one process as a deadlock victim and rolling back its transaction, allowing other transactions to proceed.

10. What is the purpose of the UPDATE_STATISTICS command?

The UPDATE_STATISTICS command updates the statistics used by the query optimizer to determine the most efficient way to execute a query. These statistics provide information about the distribution of values in an index or table column and are crucial for query performance.

11. Describe what a View is in SQL Server.

A view in SQL Server is a virtual table based on the result-set of an SQL statement. It contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.

12. What is a stored procedure in SQL Server?

A stored procedure is a prepared SQL code that you can save and reuse. Instead of writing the same code over and over again, you can create a stored procedure, and call it to execute the SQL code contained within it.

13. Explain what SQL Server Integration Services (SSIS) is.

SQL Server Integration Services (SSIS) is a platform for building enterprise-level data integration and data transformations solutions. You can use SSIS to solve complex business problems by copying or downloading files, loading data warehouses, cleansing and mining data, and managing SQL Server objects and data.

14. What are the recovery models available in SQL Server?

SQL Server offers three recovery models: Simple, Full, and Bulk-Logged. Each model dictates how transaction logs are maintained and impacts how you can restore and recover data.

15. What is database normalization?

Database normalization is the process of organizing the fields and tables of a database to minimize redundancy and dependency. Normalization involves dividing large tables into smaller tables and defining relationships between them to increase the coherence of data.

16. How do you perform a point-in-time recovery in SQL Server?

A point-in-time recovery involves restoring a SQL Server database to a specific point in time. This is achieved by restoring the full backup, the differential backup, and the transaction log backups up to the desired point of time.

17. What is the purpose of the NOLOCK hint?

The NOLOCK hint allows SQL Server to ignore locks, providing a way to read data without being blocked by other transactions. It's used to increase performance in scenarios where real-time accuracy of data is not critical.

18. How can you improve the performance of a SQL Server database?

Performance can be improved by indexing, query optimization, database normalization, updating statistics, avoiding unnecessary cursors, and configuring database files and filegroups optimally.

19. What are the differences between DELETE and TRUNCATE commands?

DELETE removes rows from a table based on the WHERE condition and can be rolled back. TRUNCATE removes all rows from a table without logging the individual row deletions, thus it's faster but cannot be rolled back.

20. What is SQL Server Reporting Services (SSRS)?

SQL Server Reporting Services (SSRS) is a server-based report generating software system that enables users to create and manage a wide range of reports. It supports various report delivery options and interactive reports.

Advance-Level Questions

1. Explain how to optimize a slow-running SQL Server query.

To optimize a slow-running query, the first step is examining the query execution plan to identify bottlenecks such as table scans, key lookups, and costly operations. Evaluating indexing strategies, including adding, modifying, or removing indexes, is crucial to improving performance. Analyzing I/O statistics and CPU usage helps pinpoint inefficiencies. Keeping statistics up-to-date is essential. Refactoring the query to simplify joins or eliminate subqueries, and using query hints selectively, can also enhance query performance.

2. Describe the process of implementing a high availability solution in SQL Server 2022.

Implementing high availability in SQL Server 2022 typically involves setting up SQL Server Always on Availability Groups, which provide failover support for multiple databases. It requires preparing the environment with Windows Server Failover Clustering on the underlying system. Configuring Availability Groups includes establishing primary and secondary replicas, setting up listener for client connections, and configuring synchronization modes—synchronous for zero data loss or asynchronous for performance optimization. Regular monitoring and testing failover scenarios are vital to ensure the system meets the required recovery objectives.

3. What are the considerations for securing SQL Server 2022?

Securing SQL Server 2022 involves multiple layers of security. At the network level, ensuring the database engine is not exposed directly to the internet and using firewall rules to limit access are crucial steps. Authentication should be managed via Windows authentication mode where possible for better security, complemented by strong password policies for SQL logins. Encrypting data at rest using Transparent Data Encryption (TDE) and securing data in transit with SSL/TLS are also recommended. Additionally, regularly applying updates and patches and conducting audits with SQL Server Audit or Extended Events to track and analyze activities are essential for maintaining security.

4. How would you handle database corruption in SQL Server 2022?

Handling database corruption involves first running the DBCC CHECKDB command to identify the extent and location of the corruption. Depending on the severity and nature of the corruption, options might include restoring from a clean backup, using the DBCC CHECKDB with the REPAIR options to fix the corruption, or manually repairing or reconstructing the affected data if possible. It's important to maintain regular, tested backups, and to isolate the cause of the corruption to prevent recurrence.

5. What are SQL Server 2022's capabilities for managing large volumes of data?

SQL Server 2022 enhances its capabilities to manage large volumes of data through features such as Columnstore indexes, which optimize large-scale data warehouse queries, and In-Memory OLTP, which improves performance for high transaction rates. Partitioning large tables and indexes can also manage data more efficiently by dividing them into smaller, more manageable pieces. Data compression features help reduce storage costs while maintaining performance. Additionally, SQL Server 2022 integrates with Big Data clusters, facilitating the management and analysis of large datasets across both structured and unstructured data sources.

6. Discuss the role of Artificial Intelligence (AI) in SQL Server 2022.

SQL Server 2022 integrates Artificial Intelligence through its built-in AI capabilities in SQL Server Machine Learning Services and SQL Server Big Data Clusters. These allow users to run Python and R scripts to perform complex analytics directly within the database engine, eliminating the need for data movement. SQL Server also offers integration with Azure Machine Learning, enabling more advanced machine learning models and AI-driven insights directly from SQL Server, enhancing decision-making processes and predictive analytics.

7. Explain the use of Dynamic Data Masking in SQL Server 2022 and its limitations.

Dynamic Data Masking (DDM) in SQL Server 2022 is used to limit sensitive data exposure by masking it to non-privileged users. It is simple to implement and does not affect database operations because the data in the database is not changed; only the output is masked. However, DDM is not a security control but a data obfuscation technique that should be used in conjunction with other security features. Limitations include the possibility for users to infer data through query patterns or mistakes in configuration, which can lead to unintentional data exposure.

8. What improvements does SQL Server 2022 offer for query performance insights?

SQL Server 2022 offers enhanced query performance insights through its Query Store feature, which now provides more detailed historical query data to help identify performance degradation and optimize query execution. The Intelligent Query Processing feature suite also contributes by automatically adapting execution plans based on changing data patterns without needing manual intervention. Additionally, SQL Server Management Studio includes more advanced tools for analyzing query performance, such as Live Query Statistics and the Performance Dashboard.

9. How does SQL Server 2022 support cloud integration?

SQL Server 2022 supports cloud integration primarily through Azure SQL Edge, enabling seamless data streaming, management, and analysis across cloud environments. It also offers enhanced Azure Hybrid Benefit options, allowing customers to use their on-premises SQL Server licenses to manage Azure SQL Database instances at reduced costs. Features like Managed Instance in Azure SQL provide near-complete compatibility for migrating on-premises SQL Server databases to the cloud, facilitating easier and more secure cloud adoption.

10 Describe the enhancements in SQL Server 2022 for disaster recovery planning.

SQL Server 2022 enhances disaster recovery planning through its improved Always On Availability Groups, which now support automatic page repair for additional reliability and easier management of disaster recovery configurations. The Accelerated Database Recovery feature significantly reduces recovery times by maintaining a persistent version store in the database, speeding up the rollback and recovery processes. SQL Server 2022 also includes better integration with Azure for disaster recovery, allowing databases to be backed up directly to Azure Blob Storage and facilitating geo-replication for global distribution and redundancy.