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T-SQL, or Transact-SQL, is Microsoft's proprietary extension to the SQL (Structured Query Language) database language. It adds several features to standard SQL such as transaction control, exception and error handling, row processing and declared variables. T-SQL is central to using Microsoft SQL Server which is an enterprise-level relational database management system. This programming language allows users to embed procedural logic and control statements into their queries for more complex operations on a server running Microsoft SQL Server.

Ask the right questions secure the right T-SQL talent among an increasingly shrinking pool of talent.

First 20 minutes

General T-SQL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in T-SQL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you declare a variable in T-SQL?

You declare a variable in T-SQL using the DECLARE statement. For example: DECLARE @MyVariable INT;

What is the purpose of the SELECT statement in T-SQL?

The SELECT statement is used to select data from a database. The data returned is stored in a result table, called the result-set.

What are the different types of JOIN in T-SQL?

The different types of JOIN in T-SQL are INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, FULL OUTER JOIN, and CROSS JOIN.

Describe the difference between UNION and UNION ALL in T-SQL.

UNION removes duplicate records (where all columns in the results are the same), UNION ALL does not.

How would you handle errors in T-SQL?

You can handle errors in T-SQL using TRY...CATCH constructs. You put the T-SQL statements that might cause an error inside a BEGIN TRY...END TRY block and the error handling code inside a BEGIN CATCH...END CATCH block.

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What you’re looking for early on

Does the candidate have a solid understanding of T-SQL syntax and commands?

Can the candidate demonstrate problem-solving skills?

Has the candidate shown an ability to work with large databases?

Is the candidate able to optimize SQL queries for better performance?

Next 20 minutes

Specific T-SQL development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What is the purpose of the UPDATE statement in T-SQL?

The UPDATE statement is used to modify the existing records in a table.

What are the different types of subquery in T-SQL?

The different types of subquery in T-SQL are: Single Row Subquery, Multiple Row Subquery, and Multiple Column Subquery.

Describe the difference between DELETE and TRUNCATE commands in T-SQL.

DELETE is a logged operation, so it can be rolled back, but it's slower. TRUNCATE is a non-logged operation, so it's faster, but it can't be rolled back.

How would you implement transaction control in your T-SQL code?

You can implement transaction control in T-SQL code using BEGIN TRANSACTION, COMMIT, and ROLLBACK statements.

What is the purpose of the INSERT INTO statement in T-SQL?

The INSERT INTO statement is used to insert new records into a table.

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At this point, a skilled T-SQL engineer should demonstrate strong problem-solving abilities, proficiency in T-SQL programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with T-SQL.

What does the following T-SQL code do?
SELECT COUNT(*) FROM Employees WHERE Salary > 50000;
This code returns the count of employees who have a salary greater than 50000.
What will be the output of the following T-SQL code?
SELECT TOP 3 * FROM Employees ORDER BY Salary DESC;
This code will return the top 3 employees with the highest salary.
What does the following T-SQL code do?
SELECT EmployeeID, FirstName, LastName, Department FROM Employees WHERE Department IN ('Sales', 'Marketing');
This code selects the EmployeeID, FirstName, LastName, and Department of all employees who work in either the Sales or Marketing departments.
What will be the output of the following T-SQL code?
BEGIN TRANSACTION; UPDATE Employees SET Salary = Salary + 5000 WHERE Department = 'Sales'; COMMIT;
This code will increase the salary of all employees in the 'Sales' department by 5000 and then commit the transaction.

Wrap-up questions

Final candidate for T-SQL Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle T-SQL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are the different types of triggers in T-SQL?

The different types of triggers in T-SQL are: DML Triggers (include AFTER triggers and INSTEAD OF triggers) and DDL Triggers.

Describe the difference between a Temporary Table and a Table Variable in T-SQL.

A Temporary Table behaves like a regular table and can have indexes, statistics, while a Table Variable can only have a primary index and does not have statistics.

How would you optimize a T-SQL query?

To optimize a T-SQL query, you can use the following strategies: limit the result set, use JOIN instead of subqueries, use UNION ALL instead of UNION, use EXISTS instead of IN, and use wildcard searching at the end of a word.

T-SQL application related

Product Perfect's T-SQL development capabilities

Beyond hiring for your T-SQL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in T-SQL projects, and can engage in multiple capacities.

T-SQL Consultive assessments

T-SQL Application Conversion Assessment T-SQL Application Integration Assessment T-SQL Data & Database Integration Assessment

Custom T-SQL development projects

Custom T-SQL App Conversion T-SQL Custom App Development Process App UI Design for T-SQL Facelifts

Hiring guide for T-SQL Engineers

T-SQL Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the T-SQL engineer at this point.

T-SQL Consultive assessments

Custom T-SQL development projects