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SQL Server Interview Questions & Answers

Basic SQL Server Concepts:

  1. Q: What is SQL Server?

    • A: SQL Server is a relational database management system (RDBMS) developed by Microsoft. It supports the storage and retrieval of data as well as various advanced features.

  2. Q: Differentiate between clustered and non-clustered indexes in SQL Server.

    • A: A clustered index determines the physical order of data in a table, while a non-clustered index does not affect the physical order of data and is stored separately.

  3. Q: Explain the purpose of the SQL Server Management Studio (SSMS).

    • A: SSMS is a graphical user interface tool used to manage SQL Server databases, including tasks such as creating databases, writing queries, and managing security.

  4. Q: How do you backup and restore a SQL Server database?

    • A: Use BACKUP DATABASE to create a backup and RESTORE DATABASE to restore it.

  5. Q: What is a stored procedure in SQL Server?

    • A: A stored procedure is a precompiled collection of one or more SQL statements that can be executed as a single unit.

SQL Server Queries:

  1. Q: Write a query to retrieve all columns from a table named "employees" in SQL Server.

    • A: SELECT * FROM employees;

  2. Q: How do you handle errors in SQL Server stored procedures?

    • A: Use TRY...CATCH blocks to handle errors and exceptions in SQL Server stored procedures.

  3. Q: Explain the purpose of the SQL Server sp_executesql system stored procedure.

    • A: sp_executesql is used to execute dynamic SQL statements or batches in SQL Server.

  4. Q: Write a query to find the second-highest salary from an "employees" table in SQL Server.

    • A: 
      SELECT MAX(salary) 
FROM employees 
WHERE salary < (SELECT MAX(salary) FROM employees);

  5. Q: What is the difference between a local and a global temporary table in SQL Server?

    • A: Local temporary tables are only accessible within the session that created them, while global temporary tables are accessible across different sessions.

Joins and Relationships:

  1. Q: Explain the concept of an INNER JOIN in SQL Server.

    • A: INNER JOIN returns rows that have matching values in both tables based on the specified condition.

  2. Q: How can you perform a self-join in SQL Server?

    • A: Use an alias to reference the same table within the query. Example: SELECT e1.name, e2.name FROM employees e1, employees e2 WHERE e1.manager_id = e2.employee_id;

  3. Q: Write a query to find duplicate records in a table in SQL Server.

    • A: 
      SELECT column_name, COUNT(*)
FROM table_name 
GROUP BY column_name 
HAVING COUNT(*) > 1;

  4. Q: Explain the purpose of the MERGE statement in SQL Server.

    • A: MERGE is used to perform insert, update, or delete operations on a target table based on the results of a join with a source table.

  5. Q: What is a Common Table Expression (CTE) in SQL Server?

    • A: A CTE is a named temporary result set that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement.

SQL Server Administration:

  1. Q: How do you monitor SQL Server performance?

    • A: Use tools such as SQL Server Profiler, Dynamic Management Views (DMVs), and Extended Events.

  2. Q: Explain the purpose of the SQL Server Agent.

    • A: SQL Server Agent is a background service that enables the scheduling and automation of tasks, such as backups and database maintenance.

  3. Q: How can you configure database mirroring in SQL Server?

    • A: Database mirroring involves creating a mirror database on a separate server and configuring a mirroring session between the primary and mirror databases.

  4. Q: What is the SQL Server Policy-Based Management feature?

    • A: Policy-Based Management allows administrators to define and enforce policies for SQL Server instances, databases, and other objects.

  5. Q: How do you create a new user in SQL Server and grant them access to a database?

    • A: 
      CREATE LOGIN username WITH PASSWORD = 'password';
USE your_database;
CREATE USER username FOR LOGIN username;

Advanced SQL Server Concepts:

  1. Q: What is the purpose of the SQL Server OFFSET and FETCH clauses?

    • A: OFFSET and FETCH are used for pagination. OFFSET specifies the number of rows to skip, and FETCH specifies the number of rows to return.

  2. Q: Explain the concept of columnstore indexes in SQL Server.

    • A: Columnstore indexes organize data into columns for better compression and query performance, especially for analytical workloads.

  3. Q: How can you implement data encryption in SQL Server?

    • A: Use features such as Transparent Data Encryption (TDE), Always Encrypted, and Cell-level Encryption for securing data.

  4. Q: What is the purpose of the SQL Server TRY_CONVERT function?

    • A: TRY_CONVERT attempts to convert a value to a specified data type, returning NULL if the conversion fails.

  5. Q: Explain the concept of the temporal table in SQL Server.

    • A: Temporal tables allow for the tracking of changes to data over time, maintaining historical versions of records.

SQL Server Security and Permissions:

  1. Q: How do you grant EXECUTE permission on a stored procedure in SQL Server?

    • A: GRANT EXECUTE ON dbo.procedure_name TO user_name;

  2. Q: Explain the purpose of the SQL Server DENY statement.

    • A: DENY is used to deny a specific permission on a securable from a principal, even if the principal has been granted that permission.

  3. Q: What is SQL injection, and how can it be prevented in SQL Server?

    • A: SQL injection is a code injection technique where an attacker can execute malicious SQL statements. Prevention involves using parameterized queries and validating user inputs.

  4. Q: How can you audit user activity in SQL Server?

    • A: SQL Server provides features like SQL Server Audit, which can be used to track and log events at the server or database level.

  5. Q: What are the differences between SQL Server roles and database roles?

    • A: SQL Server roles are server-level roles, while database roles are specific to a particular database. Server roles provide server-wide permissions, while database roles provide database-specific permissions.

SQL Server Reporting and Analysis:

  1. Q: What is SQL Server Reporting Services (SSRS)?
    • A: SSRS is a server-based reporting platform that allows the creation, deployment, and management of reports.

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. Q: Explain the purpose of the SQL Server Analysis Services (SSAS). - A: SSAS is used for online analytical processing (OLAP) and data mining functionalities, providing a multidimensional data model.

  1. Q: How can you optimize the performance of a SQL Server Reporting Services (SSRS) report?

    • A: Strategies include optimizing queries, using caching, and minimizing the use of unnecessary resources.

  2. Q: What is the purpose of the SQL Server Data Tools (SSDT)?

    • A: SSDT is an integrated development environment (IDE) used for designing, developing, and deploying SQL Server solutions, including database projects and SSIS packages.

  3. Q: How can you deploy a SQL Server Integration Services (SSIS) package?

    • A: SSIS packages can be deployed using SQL Server Data Tools or SQL Server Management Studio (SSMS).

SQL Server Best Practices:

  1. Q: What are some best practices for database maintenance in SQL Server?

    • A: Best practices include regular backups, index maintenance, statistics updates, and monitoring database growth.

  2. Q: How do you handle schema changes in a production SQL Server database?

    • A: Use version control, script changes, and test them in a development environment before applying them to production.

  3. Q: Explain the concept of the SQL Server Query Optimizer.

    • A: The Query Optimizer analyzes SQL queries and determines the most efficient way to execute them by considering factors like indexes and statistics.

  4. Q: How can you identify and resolve performance bottlenecks in SQL Server?

    • A: Use tools like SQL Server Profiler, Query Execution Plans, and Dynamic Management Views (DMVs) to identify and address performance issues.

  5. Q: What is the purpose of the SQL Server Database Engine Tuning Advisor?

    • A: The Database Engine Tuning Advisor helps optimize query performance by analyzing workloads and recommending indexes and statistics.

Troubleshooting and Maintenance:

  1. Q: How do you troubleshoot a slow-performing query in SQL Server?

    • A: Use tools like SQL Server Profiler, Execution Plans, and DMVs to identify the cause of performance issues.

  2. Q: What is the purpose of the SQL Server Error Log?

    • A: The Error Log records messages related to SQL Server events, errors, and informational messages.

  3. Q: How can you shrink a SQL Server database?

    • A: Use the DBCC SHRINKDATABASE or DBCC SHRINKFILE commands. However, shrinking databases should be done cautiously due to potential fragmentation.

  4. Q: What is the purpose of the SQL Server Resource Governor?

    • A: The Resource Governor enables the allocation and management of resources, such as CPU and memory, for different workloads and applications.

  5. Q: How do you monitor deadlock occurrences in SQL Server?

    • A: SQL Server Profiler and Extended Events can be used to capture and analyze deadlock information.

Industry Trends and New Features:

  1. Q: What are some of the new features introduced in the latest version of SQL Server?

    • A: Features may include enhancements to security, performance improvements, and new capabilities in areas like analytics and machine learning.

  2. Q: How can SQL Server be integrated with cloud services like Azure?

    • A: SQL Server can be hosted on Microsoft Azure as a virtual machine (Azure SQL VM) or use Azure SQL Database, a fully managed database service.

  3. Q: Explain the concept of PolyBase in SQL Server.

    • A: PolyBase allows for querying data stored in Hadoop or Azure Blob Storage from within SQL Server.

  4. Q: What is the role of SQL Server in a hybrid cloud environment?

    • A: SQL Server in a hybrid cloud environment can provide seamless integration between on-premises and cloud databases, allowing for flexibility and scalability.

  5. How can you ensure high availability in SQL Server?

    • A: Options for high availability include database mirroring, failover clustering, log shipping, and Always On Availability Groups.