When hiring SQL Server developers, conducting a thorough interview process is essential to finding the right candidate. As an interviewer, you should ask thoughtful questions to assess candidates’ technical skills, problem-solving abilities, soft skills, and personality. A well-rounded interview will help you gauge a candidate's expertise in SQL Server development, ability to handle complex tasks, and compatibility with your team.
Revelo can partner with you throughout this process. With our talent-sourcing expertise, we can help you find top-tier SQL Server developers to interview, schedule and coordinate the interviews, and coach you through them to help make the entire process smoother.
In this article, you’ll learn what SQL Server developers do and discover a wide range of junior-, mid-, and senior-level SQL Server interview questions and answers to help you assess candidates’ suitability for your company.
What Is an SQL Server Developer?
SQL Server developers are tech professionals who specialize in working with Microsoft SQL Server, a widely used relational database management system. These developers design, develop, and maintain SQL databases and write efficient SQL queries to retrieve and manipulate data.
SQL Server development involves a variety of tasks. Developers work on database design and architecture, creating tables, and defining relationships between them. Developers also write complex SQL queries to extract information from a database, perform data transformations and aggregations, and optimize query performance. Additionally, SQL Server developers develop stored procedures, triggers, and functions to automate database operations and ensure data consistency.
Hiring an SQL Server developer is a good idea when your organization deals with a large amount of data that must be efficiently stored, managed, and queried. SQL Server developers can help to streamline the data retrieval and manipulation processes, making extracting meaningful insights and supporting business decision-making easier. Using SQL Server developers can also ensure your databases integrate smoothly with other applications.
Junior-level SQL Server Developer Interview Questions
When interviewing junior-level SQL Server developers, you should ask fundamental SQL interview questions that assess their knowledge and capabilities. You can use these technical questions to gauge their understanding of SQL syntax, SQL statements, and basic database concepts like joins and primary keys. By asking these questions, you can evaluate their proficiency, problem-solving skills, and ability to apply SQL principles to real-world scenarios.
What is the difference between an INNER JOIN and an OUTER JOIN in SQL?
SQL Server developers use join operators to combine related data in various ways. INNER JOIN and OUTER JOIN are the two major join categories in SQL. The INNER JOIN operator returns only the matching rows between two tables based on a specified condition, while the OUTER JOIN returns not only the matching rows but also the non-matching rows from one or both tables.
A candidate’s answer to this question is important because it demonstrates their knowledge of SQL syntax, query construction, and data from multiple tables.
What is the purpose of the GROUP BY clause in SQL?
Developers use the GROUP BY clause to group rows with the same values. GROUP BY is typically used with aggregate functions, such as COUNT, SUM, and AVG.
You can use this question to assess a candidate's understanding of data grouping and aggregation in SQL; it gives a candidate a chance to demonstrate their knowledge of query manipulation and data analysis and their ability to generate meaningful insights from large datasets. You can also use a candidate’s answer to evaluate their proficiency in SQL functions and ability to translate business requirements into SQL queries.
What is a primary key in SQL, and why is it important?
A primary key is a unique identifier for a specific row in a table in SQL. Developers use primary keys to ensure data integrity by enforcing uniqueness. A primary key also serves as a reference for relationships with other tables.
This question is important because it helps you assess a candidate's understanding of database design principles and their familiarity with key SQL concepts. The question also tests a candidate’s data integrity knowledge and ability to define and implement primary keys correctly when they write an SQL query. A candidate’s answer demonstrates their knowledge of database performance optimization because primary keys are often used for indexing and efficient data retrieval.
Mid-level SQL Server Developer Interview Questions
When interviewing a candidate for a mid-level SQL Server developer position, you should ask questions that assess a candidate's depth of knowledge and experience. These questions should focus on advanced SQL concepts, query optimization, stored procedure, database design, and troubleshooting skills. By asking such questions, you can gauge the candidate's ability to handle complex database scenarios, understanding of performance tuning techniques, familiarity with advanced SQL features, and problem-solving skills in a SQL environment.
What is the difference between UNION and UNION ALL in SQL?
SQL Server developers use UNION and UNION ALL to combine the result sets of multiple SELECT statements. The two operators handle duplicate records in different ways. Mid-level developers should know that UNION eliminates duplicate rows while UNION ALL retains all rows, including duplicates.
You can use this question to assess candidates' understanding of SQL query optimization and knowledge of different set operations. The question tests a candidate’s ability to make informed choices between UNION and UNION ALL based on specific requirements, such as data integrity or performance when dealing with large result sets.
Describe a situation in which you had to optimize the performance of a SQL server database, including your steps and the outcome.
An experienced candidate can describe a specific situation in which they identified performance issues related to SQL, implemented optimization techniques, and measured the resulting improvements. They should be able to discuss analyzing query execution plans, clustered indexing strategies, non-clustered indexing strategies, query rewriting, and database server configuration changes.
A candidate’s answer to this prompt will demonstrate their knowledge of SQL Server performance tuning techniques, their problem-solving skills in addressing performance bottlenecks, constraints in SQL, and their ability to measure and communicate the impact of their optimizations.
What are “included columns” used for in SQL Server indexing?
Included columns in SQL Server indexing are non-key columns that are stored with the index. Included columns enhance query performance by covering more columns in the index, reducing the need to access the actual server table data in the SQL server. Mid-level SQL server developers should be familiar with included columns. Developers use included columns because they allow them to optimize query performance by carefully selecting which non-key columns to include in a clustered index or non-clustered index.
A candidate’s answer to this question demonstrates whether they know how to improve query execution times and enhance overall database performance.
Senior-level SQL Server Developer Interview Questions
When interviewing a senior-level SQL Server developer, you should ask questions about their experience in leading database projects, managing teams, optimizing performance at scale, and resolving complex database issues. Candidates’ answers to these questions show their expertise in database architecture, ability to mentor junior developers, problem-solving skills, and overall depth of experience in working with SQL Server in high-impact scenarios.
When would you use the WITH CHECK OPTION to create a view?
SQL Server developers use the WITH CHECK OPTION to create views in ways that ensure the modifications made to the views follow the specified conditions. Senior developers should know when and how to use the WITH CHECK OPTION to ensure the accuracy and consistency of data within the views, enhancing the overall quality and reliability of the database system.
What are examples of errors that the CATCH block can't handle?
Developers use the T-SQL TRY… CATCH construct to create an error-handling mechanism. T-SQL is an extension of the SQL language that Microsoft SQL Server uses.
When an error occurs within the TRY block, control transfers to the CATCH block, which responds in a logical way to the error. But certain errors are not affected by the TRY… CATCH construct. Examples include errors with a severity of 10 or lower (in informal messages) and a severity of 20 or higher (indicating fatal errors and system problems). Additionally, the TRY… CATCH construct doesn't trap interrupted client requests, killed sessions, or broken client connections.
Knowing this information demonstrates a senior-level SQL Server developer’s deep understanding of error-handling mechanisms in T-SQL.
How do AFTER and INSTEAD OF triggers differ?
Triggers are automatic responses to special database-related events. AFTER triggers execute after the triggering action has occurred, while INSTEAD OF triggers execute instead of the triggering action. You can use INSTEAD OF to prevent user errors, such as a user trying to insert a prohibited value into a table.
Senior-level SQL Server developers should know the difference between AFTER and INSTEAD OF. You can use this question to test a candidate's knowledge of advanced trigger concepts and ability to choose the appropriate type of SQL trigger for different scenarios, ensuring accurate data manipulation and maintaining data integrity within a database.
Hire SQL Server Developers With Revelo
Sourcing, vetting, and hiring SQL Server developers can be challenging, but Revelo can help. Our tech talent platform connects you with highly qualified developers who have undergone rigorous vetting for technical skills, soft skills, and English-language proficiency. With timezone alignment and comprehensive support in payroll, benefits administration, taxes, and local compliance, Revelo ensures a seamless hiring experience.
Contact us today to find a top SQL Server developer and streamline your recruitment process.