40 SQL queries interview questions to ask software engineers

Do you need to hire an SQLite developer for your team? To ensure you don’t hire the wrong candidate, you will need an effective strategy to assess your applicants. 

One method to assess specific skills is to use our SQLite Coding test in an SQL assessment. Another approach is to complete a formal interview. But what questions on SQL queries should you ask applicants?

In this article, we will provide 40 SQL queries interview questions you can ask software engineering candidates. Just take a look at the lists below and choose the right questions for your hiring process.

10 SQL queries interview questions related to definitions and operators

Ask interviewees a few of these 10 SQL queries interview questions related to definitions and operators to test your candidates’ entry-level knowledge.

1. What are SQL operators?

2. Can you give us a definition and example of string operators in SQL?

3. Can you explain what compound operators are in SQL?

4. Can you explain what arithmetic operators are in SQL?

5. Can you define comparison operators in SQL?

6. Can you tell us what logical operators are in SQL?

7. Can you give me a definition of bitwise operators in SQL?

8. Do you understand what the >= operator does in SQL?

9. Describe what the !< operator does in SQL.

10. Explain what the + arithmetic operator does in SQL.

5 SQL queries interview questions and answers related to definitions and operators

Check the answers to these five interview questions on SQL queries to evaluate your candidates’ responses and assess their technical know-how.

1. What are SQL operators?

SQL operators are words or characters developers use to query a database with an SQL expression. They contain keywords that help developers access data and receive a result based on the function of the operator. 

Check to see if your candidates know that developers use many operators to manipulate data – those who can name a few examples are ones to consider for your vacancy.

2. Can you give us a definition and example of string operators in SQL?

Developers use string operators for concatenation or to combine two or more strings. Some examples of data types developers can combine into one expression with string operators include:

• Character strings

• Columns

• Strings and column names

When you hire a developer, you could consider assessing them more closely by checking if they can define character strings, columns, and strings.

3. Can you explain what compound operators are in SQL?

Compound operators enable developers to execute operations and set a unique value to the operation’s result. If they have used compound operators in their work, developers will know that there are several types of compound operators, such as:

• += This add assignment compound operator adds an amount to the original value and gives a unique value to the result

• -= This subtract assignment compound operator subtracts an amount from the original value and gives a unique value to the result

• *= This multiply assignment compound operator multiplies the value by an amount and gives a unique value to the result

4. Can you explain what arithmetic operators are in SQL?

Software engineers and database professionals use arithmetic operators to run mathematical operations for two expressions of different data types. They run them from the numeric data type category. 

To show their expertise, applicants should explain some, if not all, of the arithmetic operators, which include the following:

• + Addition

• - Subtraction

• * Multiplication

• / Division

5. Can you define comparison operators in SQL?

If developers want to test if two expressions are the same, they can use a comparison operator. They can use this type of operator on all expressions, with a few exceptions. For example, developers cannot use them for text, image, or ntext data types.

Consider if your applicants can name a few examples of comparison operators in SQL, such as the following:

• > Greater than

• < Less than

• > = Greater than or equal to

• < = Less than or equal to

20 SQL queries interview questions and answers to assess your developers’ skills

Ask your interviewees some of the following SQL queries interview questions and check their responses against the answers we provide.

1. Write a query to fetch a candidate ID and the first name of all applicants who applied to company XYZ.

Applicants can fetch the candidate details with a where clause for the company. This clause is ideal for filtering records.

An example of a query your applicants might write is:

SELECT CandidateID, FirstName

FROM CandidateDetails

WHERE CompanyID = XYZ

2. Which SQL query would you write to fetch various projects from the employee responsibilities table? 

Check if candidates understand that the distinct clause will help them fetch the data from the employee responsibilities table, which contains values for each employee. The distinct clause returns different values instead of duplicates. 

Candidates may use the following query to answer this problem:

SELECT DISTINCT (Project)

FROM EmployeeResponsibilities

3. Can you write a query to fetch the number of employees working in project ‘ABC’ from the employee data table?

Knowledgeable applicants will understand that they should use their query’s aggregate function count() and the where clause to fetch the required results. The count() function returns the rows that match the developer’s criterion:

SELECT Count(*)

FROM EmployeeData

WHERE Project = ‘ABC’;

4. How would you structure a query to find candidates’ average, maximum, and minimum salaries?

The best responses will mention that engineers should use the aggregate SQL function to fetch these values. They should structure the query in a similar way to the following example:

SELECT Avg(Salary),

Max(Salary),

Min(Salary)

FROM CandidateSalary;

5. Can you write a query to help you find the ID of a candidate whose salary is between $50,000 and $80,000?

Do your candidates know their query should feature the between operator and where to retrieve the correct information? Skilled applicants will understand that the between operator selects values within the range specified by the engineer. One example of a query that meets these requirements is:

SELECT CandidateID, Salary

FROM CandidateDetails

WHERE Salary BETWEEN 50000 AND 80000;

6. Which query would you use to fetch candidates who live in London and work for “DEF”?

Applicants with beginner SQL knowledge should know that to satisfy the conditions (the geographical location and the company), they should use the AND operator in their query. The AND operator is ideal for filtering data and retrieving precise results:

SELECT CandidateID, City, CompanyID

FROM CandidateDetails

WHERE City = ‘London’ AND CompanyID = ‘DEF’;

7. Write an SQL query to fetch candidates who live in Edinburgh and work for “GHI.”

Candidates who know SQL operators will understand that they should use the OR operator to fetch the correct data. Here is an example query they may produce:

SELECT CandidateID, City, CompanyID

FROM CandidateDetails

WHERE City = ‘Edinburgh’ OR CompanyID = ‘GHI’;

8. Which query would you write to fetch all applicants who complete tasks for projects other than “KeyProject2”?

Applicants should use the NOT operator to fetch table rows that do not satisfy the condition. A couple of alternatives are available for answering this question. Some candidates may provide the following answer:

SELECT ApplicantID

FROM ApplicantDetails

WHERE NOT Project = ‘KeyProject2’;

Other candidates may use the “not equal to” operator to write a different query that achieves the same outcome:

SELECT ApplicantID

FROM ApplicantDetails

WHERE Project <> ‘KeyProject2’;

9. Write a query to fetch candidates with names that begin with three characters, the text “sf”, and end with any characters.

Applicants should use the ‘_’ operator and the ‘%’ wild card to write this SQL query. They should know they can use the ‘_’ operator to match a single character and the “%” wild card to match zero or several characters:

SELECT FullName

FROM CandidateDetails

WHERE FullName LIKE ‘_sf%’;

10. Can you write us a query to fetch the candidate IDs in either the candidate details or the candidate salary table?

In this case, the best way to fetch unique employee IDs from both tables is to use the union clause. Check if candidates know this clause combines the results from two SQL queries and returns unique rows.

SELECT CandidateID FROM CandidateDetails

UNION

SELECT CandidateID FROM CandidateSalary;

11. Which query would you write to fetch records that one table contains but another does not?

Do your programmer applicants understand that the minus operator is the ideal option to complete this query? Can they provide an example of a workable query that fetches the correct records? They may write something similar to the following:

SELECT * FROM CandidateSalary

MINUS

SELECT * FROM ShortlistedSalary;

12. Which query is best to fetch candidate IDs that the candidate details and candidate salary contain?

Applicants may use a subquery to retrieve this data from the tables. Here is an example of a query that contains a subquery they might use:

SELECT CandidateID FROM CandidateDetails

WHERE CandidateDetails IN

(SELECT CandidateID FROM CandidateSalary);

13. Which query and function would you use to fetch a candidate’s full name and replace the space with a hyphen ‘-’

A function that can help applicants fetch a candidate’s full name from the table and replace the space with a hyphen is the replace function. They can use this function in a query such as the following:

SELECT REPLACE(FullName, ‘ ’, ‘-’)

FROM CandidateDetails;

14. Could you write us a query to show the candidate and company ID together?

Candidates must know the concat command to write a query that fetches this information. The concat command adds two or more strings together. Here is an example query candidates may use:

SELECT CONCAT(CandidateID, CompanyID) as NewID

FROM CandidateDetails;

15. Which query would you write to change candidates’ names to uppercase and the country they’re from to lowercase?

SQL has two functions for changing the letter case: the upper and lower functions. Candidates should produce a similar query to this one to achieve the output:

SELECT UPPER(FullName), LOWER(Country)

FROM CandidateDetails;

16. Write a query to fetch all candidates not completing side projects.

Applicants should mention that the null operator is essential for this basic SQL queries interview question. The null operator helps engineers test for empty values. They can write a query such as the following to meet the requirements:

SELECT CandidateID

FROM CandidateDetails

WHERE SideProject IS NULL;

17. Write down a query that fetches the names of candidates who have a salary greater than or equal to $6,000 and less than or equal to $11,000.

In the best queries for this problem, a combination of the between operator and the where clause will return the candidate IDs of candidates whose salaries meet the criteria – candidates should combine this structure with a subquery, such as in the following example:

SELECT FullName

FROM CandidateDetails

WHERE CandidateID IN

(SELECT CandidateID FROM CandidateSalary

WHERE Salary BETWEEN 6000 AND 11000);

18. Write an SQL query to fetch all candidate details of those who attended the interview process in March 2023 from a candidate details table.

The query with which candidates should respond when they answer this SQL queries interview question should contain the between operator and include the date range mentioned in the question. It should look something like the following example:

SELECT * FROM CandidateDetails

WHERE DateOfAttending BETWEEN ‘01/03/2023’

AND ‘31/03/2023’

19. Do you have a query to fetch all the candidate records in the candidate salary table?

Skilled candidates should know that SQL engineers can use the exists operator to retrieve candidate records in the candidate salary table. Check if your applicants can explain that the exists operator tests if a record exists.

SELECT * FROM CandidateDetails C

WHERE EXISTS

(SELECT* FROM CandidateSalary S

WHERE C.CandidateID = S.CandidateID);

20. Could you write a query to join three tables together?

Candidates with entry-level SQL experience should understand that two join clauses can help engineers join three tables. 

SELECT column3, column4

FROM TableX

JOIN TableY ON TableX.Column 5 = TableY.Column5

JOIN TableZ ON TableX.Column 6 = TableZ.Column6;

10 SQL queries interview questions related to skills and abilities

Ask interviewees a few of these 10 interview questions to assess candidates’ skills, abilities, and experience working with SQL queries.

1. Would you say you have good attention to detail as an SQL engineer?

2. How would your engineering manager rate your problem-solving abilities?

3. Give us a rating of your critical-thinking skills and an example of its usefulness.

4. How would your engineering manager rate your time-management skills?

5. Give us a rating of your project-management skills.

6. How would you rate your PostgreSQL skills?

7. Would you say you have good database-management skills?

8. How would your engineering manager rate your database-development skills?

9. How would you rate your RDBMS knowledge?

10. Explain why communication skills are essential for SQL developers.

5 SQL queries interview questions, and answers related to skills and abilities

Check out our sample answers to five of the above SQL queries interview questions to help you evaluate your candidates’ responses.

1. How would your engineering manager rate your database-development skills?

If you are hiring an applicant who will work on database development using SQL queries, it’s crucial to check how they rate their database-development skills.

Applicants should know how to complete transactions, index, optimize, and use data models to meet your company’s needs. Therefore, you may consider asking follow-up questions about these specific duties, such as, “Tell me about your database indexing knowledge using Oracle,” to learn about your candidates’ expertise

If you need to assess your candidates’ database-development skills, you can use our Database Development test in your SQL assessment. 

2. How would you rate your PostgreSQL skills?

Some development work requires programmers to understand relational database management systems such as PostgreSQL. Since developers require the SQL programming language to use PostgreSQL, it is crucial to test both skills and check if your applicant has the right PostgreSQL abilities.

Ask candidates the right questions to learn if they understand how to:

• Monitor and tune the performance of this system with SQL

• Ensure high availability

• Complete administrative duties

You can also test their abilities with our PostgreSQL test. The test is ideal for intermediate-level PostgreSQL administrators.

3. Give us a rating of your project-management skills.

Most software developers must manage projects efficiently, and SQL developers must also handle this task. Efficient project management can help software development teams:

• Produce a higher output

• Advance in their career

Project-oriented roles such as software development rely on project-management methods, like the Waterfall, Kanban, and Agile strategies. It’s essential to check if applicants have project-management skills and experience with these methods. 

Review how highly your applicants rate their project-management skills. And If you need to assess these skills, look no further than our Project Management skill test. 

4. How would you rate your DBMS knowledge?

Developers must use the SQL programming language to query data from DBMSs (database management systems). If they understand the link between SQL queries and DBMSs, they will face fewer problems when they:

• Manage data 

• Update data

• Delete data

If you need to assess your applicants’ knowledge of DBMS systems, such as Oracle, you can test them with our Oracle DBMS test

5. Explain why communication skills are essential for SQL developers.

Communication is an essential skill for SQL developers. Written and verbal communication skills are necessary for developers who meet with stakeholders, present concepts to clients, and share ideas with their team.

With the right communication style, developers can enhance the company’s professionalism and output by clarifying project expectations.

Test your applicants’ communication skills with our Communication skill test. It will help you assess their:

• Written communication etiquette

• Spoken communication

• Skills in clarifying the next steps

When should HR professionals use SQL queries interview questions?

The best way to use interview questions on SQL queries is to wait until applicants complete your SQL assessment. Asking applicants to complete the tests in the assessment first will enable you to create a shortlist quickly and avoid screening resumes.

It’s an excellent strategy to help you mitigate unconscious bias and avoid hiring the incorrect applicant for the job. You can also keep your recruitment metrics, such as time-to-hire, low and receive some suggestions for interview questions from your applicants’ skills assessment.

Find SQL developers with SQL queries interview questions 

Finding an SQL developer that matches your requirements is simpler than you might assume. The easiest method is to use SQL query interview questions and skill tests to assess your candidates.

Experts create our SQLite Coding test to give non-technical recruiters the support they need to hire a developer without stress or concern.

Try TestGorilla for free and use our tests and interview questions to hire the right expert for your team.