Hiring guide for Transact-SQL Engineers

Transact-SQL Developer Hiring Guide

Transact-SQL, often abbreviated as T-SQL, is Microsoft's proprietary extension to the SQL (Structured Query Language). It is used to interact with relational databases and adds several features to standard SQL, including transaction control, exception and error handling, row processing, and declared variables. T-SQL is central to using Microsoft SQL Server, a comprehensive database platform providing enterprise-class data management and business intelligence tools. It allows users to embed procedural logic and control statements into their SQL code, making it more powerful and flexible for complex operations.

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

First 20 minutes

General Transact-SQL app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Transact-SQL application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you define a primary key in SQL?
A primary key can be defined in SQL using the PRIMARY KEY constraint. This can be done during the creation of the table using the CREATE TABLE statement, or later using the ALTER TABLE statement. The syntax is: CREATE TABLE table_name (column1 datatype, column2 datatype, ..., PRIMARY KEY(column));
What are SQL Joins?
SQL Joins are used to combine rows from two or more tables, based on a related column between them. There are four types of Joins in SQL: INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
Describe the difference between DELETE and TRUNCATE commands in SQL.
DELETE is a DML command and can be rolled back. It is used to delete specific rows from a table. TRUNCATE is a DDL command and cannot be rolled back. It is used to delete all rows from a table.
How would you use the SELECT statement in 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. The syntax is: SELECT column1, column2, ... FROM table_name;
What are SQL Views?
A view is a virtual table based on the result-set of an SQL statement. A view 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.
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What you’re looking for early on

Does the candidate have a strong understanding of Transact-SQL syntax and commands?
Can the candidate demonstrate experience with database design and normalization?
How well does the candidate understand stored procedures, functions, and triggers?
Is the candidate able to troubleshoot and optimize SQL queries?

Next 20 minutes

Specific Transact-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.

Describe the difference between a clustered and a non-clustered index in SQL.
A clustered index determines the physical order of data in a table, whereas a non-clustered index does not alter the physical order of data, but creates a logical order that is presented to the user.
How would you handle errors in SQL Server?
Errors in SQL Server can be handled using the TRY...CATCH construct. It allows you to separate the action of the code from the error handling. If an error occurs in the TRY block, control is passed to another group of statements in the CATCH block.
What are stored procedures in SQL?
Stored procedures are prepared SQL codes that you can save, so the code can be reused over and over again. They can be used to perform specific actions in the database, such as reading, writing, modifying, and deleting data.
Describe the difference between UNION and UNION ALL in SQL.
UNION operator is used to combine the result-set of two or more SELECT statements, but it eliminates duplicate rows. UNION ALL does the same, but it does not remove the duplicate rows.
How would you optimize a SQL query?
SQL query optimization can be done by reducing the use of full table scans, using indexes where appropriate, limiting the result set by using WHERE and LIMIT clauses, and avoiding the use of wildcard characters at the beginning of a LIKE pattern.
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The ideal back-end app developer

What you’re looking to see on the Transact-SQL engineer at this point.

At this point, a skilled Transact-SQL engineer should demonstrate strong problem-solving abilities, proficiency in Transact-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 Transact-SQL.

What does the following SQL statement do?
SELECT COUNT(*) FROM Employees WHERE Salary > 50000;
This statement counts the number of employees in the 'Employees' table who have a salary greater than 50000.
What will be the output of the following SQL command?
This command will return the top 3 employees with the highest salary from the 'Employees' table.
What does the following SQL statement do?
SELECT AVG(Salary) FROM Employees WHERE DepartmentId = 1;
This statement calculates the average salary of employees in the 'Employees' table where the DepartmentId is 1.
What will be the output of the following SQL command?
SELECT EmployeeId, COUNT(*) FROM Employees GROUP BY EmployeeId HAVING COUNT(*) > 1;
This command will return the EmployeeId and count of employees from the 'Employees' table where the same EmployeeId appears more than once.

Wrap-up questions

Final candidate for Transact-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 Transact-SQL application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What are SQL Triggers?
A trigger is a special type of stored procedure that is executed when an INSERT, DELETE or UPDATE statement modifies data in a table. SQL Server initiates an AFTER INSERT trigger whenever an insert statement event occurs.
Describe the difference between a TEMPORARY table and a TABLE variable in SQL.
A TEMPORARY table is a special type of table that is automatically deleted when the session that created it ends. A TABLE variable is a type of variable that is used to store a result set for processing at a later time.
How would you implement transaction control in SQL?
Transaction control in SQL can be implemented using the commands BEGIN TRANSACTION, COMMIT, and ROLLBACK. BEGIN TRANSACTION marks the starting point of an explicit or implicit transaction. COMMIT saves any transactional changes and ends the transaction. ROLLBACK undoes any changes made in the current transaction.

Transact-SQL application related

Product Perfect's Transact-SQL development capabilities

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