Top scenario-based SQL interview questions to ask programmers

Structured Query Language or SQL is the foundation of data management for organizations today. For any database professional, mastering the concepts and applications of SQL is crucial for interacting with data and performing data manipulation tasks.

This blog will discuss scenario-based SQL interview questions for successful hiring outcomes.

Instead of testing candidates for their ability to memorize syntax, using scenario-based SQL questions allows interviewers to evaluate if candidates can practically apply their SQL knowledge in real-world situations. Scenario-based SQL interview questions and answers require candidates to analyze complex problems and come up with solutions using SQL queries. These realistic scenarios help recruiters to gauge candidates’ understanding of database concepts, critical thinking skills, and problem-solving skills.

Importance of scenario-based SQL interview questions

• Assessment of practical application

General SQL interview questions are designed to test the theoretical knowledge of candidates. However, using scenario-based SQL questions offers candidates an opportunity to showcase their practical proficiency and ability to apply their SQL skills in real-world scenarios.

• Job simulation

Presenting real-world scenarios as SQL interview questions is a great way for employers to understand how well candidates can handle challenges encountered in the job role. For experienced professionals, scenario-based SQL questions can be a performance predictor, offering insight into their actions, responses, and approaches.

• Assess the approach to problem solving

Scenario-based SQL interview questions help gauge the approach candidates take to problem-solving and evaluate their critical thinking skills in the context of database administration.

• Knowledge of database concepts

These interview questions can also assess candidates’ understanding of database concepts like database design, manipulation, and data analysis, which are essential competencies that any database professional should possess.

• Decision making

Scenario-based SQL interview questions can indicate the potential of candidates to make data-driven decisions, which is a highly valued trait for organizations.

1. What is the function for converting seconds into the time format?
2. What query can be used to display the number of weekends in a specified month?
3. There are two tables that cannot be joined. How to display records that are common on both tables?
4. What query will display the third-last record from a table?
5. What is the query that can be used to convert a date into the DD-MM-YYYY format?
6. How to drop all user tables from Oracle using a query?
7. What query can be used to view the maximum salary of employees in a specific department in a month-wise format?
8. How to display the second-highest salary in an employee table?
9. Write a query to create a list of all employees and their managers.
10. What query can be used to find the last day of the previous month?
11. How to find a student’s admission date and display it in a Year-Day-Date format using a query?
12. What query will create a new table with the ‘student table’ structure?
13. Write a query for viewing records that are common between two different tables.
14. What query can be used to view the monthly salaries of employees based on their annual salaries?
15. What query can be used to view the number of values in a student table, if the values in the table are separated by commas?
16. Which query helps retrieve information of employees who have not been assigned to any department?
17. Write a query using the rank function to display the third-highest salary.
18. Which query can display all employees with a salary higher than a certain amount, who joined in 2022?
19. Display a string vertically using a query.
20. Display the first 25% of records of a student table.
21. Use a query to display the last 30% of student table records.
22. Which query can convert system time into seconds?
23. Write a query to display numbers from 1 to 100.
24. How to display the DDL of any table?
25. Display only odd rows from the student table.
26. How to explain what a database is to another employee?
27. Explain the difference between RDBMS and DBMS to another employee who has no knowledge of SQL server or database management.
28. Use an SQL query to select unique records in a table.
29. Which SQL query will delete duplicate records in a table?
30. Read the top five records of a database using an SQL query.

1. How to explain what a database is to another employee?

Organizations are made up of different departments and teams, with employees with different skill sets. This workforce can be more productive when there’s effective communication between cross-functional teams. For this reason, programmers should be able to support employees who may not have the same level of knowledge about the technical aspects.

The ideal candidate should be able to explain that a database refers to a collection of structured data that can be stored, managed, accessed, and retrieved in a computer system, file system, computer cluster, or cloud storage, depending on the size. The more straightforward and easier it is to understand their explanation, the better they will be at communicating with other teams and departments.

2. Explain the difference between RDBMS and DBMS to another employee who has no knowledge of SQL server or database management. 

It is important to assess whether candidates can explain complex SQL topics in a way that even someone with no idea about database management can understand easily. Recruiters must ensure that candidates answer such questions using layperson terms and clear language.

Their answer should effectively convey that a DBMS is a database management system, and it enables people to manage databases or retrieve information from databases. A DBMS structures and organizes data to make it easy to access. However, only single data elements can be accessed at a time using a DBMS. On the other hand, an RDBMA structures data into a table format, which allows you to access multiple data elements in one go.

3. Use an SQL query to select unique records in a table.

Such questions are practical SQL interview questions and answers should not take time. This question can help recruiters assess whether candidates understand SQL queries and can convey technical information clearly.

There are a few acceptable answers to this question. The GROUP BY function allows you to view unique records from specific columns and query them, so candidates may suggest using the GROUP BY and SELECT queries to collect information from multiple records and group them by columns.

Another way is by using the ROW_NUMBER() function to number the rows of the result, which will work by assigning row numbers to unique records for the query.

4. Which SQL query will delete duplicate records in a table? 

Reducing the amount of duplicate data and streamlining the database can free up storage space and speed up data-retrieving processes, while databases filled with duplicate records can even impact the processing speed of the computer. Candidates should know how this basic task is to be performed using an SQL query.

One of the ways in which duplicate records can be deleted is by using GROUP BY and HAVING to retrieve duplicate records and store them in a subquery or temporary table, which then can be removed from the original table using the DELETE statement.

Recruiters should look for candidates who are able to provide multiple solutions for the task and can describe when each solution should be used.

5. Read the top five records of a database using an SQL query.

Skilled candidates should be able to retrieve the top five records of any database and answer this question quickly. Candidates should mention the ROWNUM function, which enables allocating a numbered order to the results using a pseudo column.

1. Which SQL query can be used to read the last five records of a database?
2. What query helps display the 15th highest salary from an employee table?
3. What is an execution plan and when is it needed?
4. How is UNION different from UNION ALL?
5. How many joins are supported in SQL?
6. Use a self-join to find the fifth-highest score in a student table.
7. What query helps display the number of employees who joined the organization in the last five years?
8. How to select all records in a student table, excluding specific columns or criteria?
9. How to get the DDL of a table?
10. Which query displays the Nth record from a student table?

1. Which SQL query can be used to read the last five records of a database?

The solution to this is similar to how the top five records are found using the ROWNUM function. However, candidates should also mention using the ‘minus’ factor to pull the last five records instead of the first five.

2. What query displays the 15th highest salary from an employee table?

SQL interview questions like this help recruiters get an idea of how fast candidates can work and how productive they can be. This question requires candidates to quickly develop an SQL query and test it. Asking the candidates to explain their answer can also help understand their reasoning and approach to solving the problem.

3. What is an execution plan and when is it needed?

Execution plans are guides that dictate the server’s query optimizer’s selected methods of data retrieval. An execution plan is used by SQL professionals to analyze the efficiency of stored procedures and it enables programmers to gain an understanding of query procedures to optimize performance.

4. How is UNION different from UNION ALL?

Candidates should be able to differentiate between these two SQL operators. UNION combines multiple datasets into one and removes any duplicate rows from the result. UNION ALL also combines multiple datasets into one, but it does not remove the duplicate rows.

5. How many joins are supported in SQL?

Candidates should ideally be able to list all joins supported in SQL – INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN, and CROSS JOIN. Candidates can also be asked to provide examples of when each join should be used to evaluate their level of experience and practical proficiency.

1. Fetch the last record from a table using a query.
2. When is a linked server used and why?
3. What are the different types of authentication modes?
4. Write a single query to add email validation.
5. Where are usernames and passwords stored in an SQL server?
6. What can be done when it is not possible to find the correct query for a problem at hand?
7. Which interview questions today were the most difficult to answer? Why?
8. Do you have other relevant programming knowledge that we should know of?

1. Fetch the last record from a table using a query.

It is best to provide candidates with a sample table for which they are required to write a query, so they can test it as well.

2. When is a linked server used and why? 

These types of SQL interview questions help assess the strategic knowledge of candidates that directs their decision-making. Candidates should know linked servers are used to link to remote databases and asking them when they should use linked servers can help recruiters evaluate whether candidates just know how to write SQL queries or if they have actual practical experience.

3. What are the different types of authentication modes?

Candidates should describe the two primary authentication modes supported by SQL servers: Windows authentication and mixed mode. Apart from the description of the modes, candidates can also be asked for their experience in using these modes and if they can explain what each does.

4. Use only one query to add email validation.

Candidates should not only write a query to add email validation, but they should also specify the RDBMS with which the query is compatible. For example, for the Microsoft SQL server, the query will be PATINDEX(‘%[^a-z,0-9,@,.,_]%’, REPLACE(email, ‘-‘, ‘a’)) = 0;.

5. Where are usernames and passwords stored in an SQL server?

Candidates should be able to explain clearly that usernames and passwords are not stored in a text format but in a hashed format for enhanced security, and that they can be found in the sysxlogins table in the master database.

• Data engineer
• Data analyst
• Business analyst
• Business intelligence developer
• Software developer
• Database architect
• Database administrator

There is a high demand for SQL professionals in the world, and there is also a large number of applicants for these job openings. That is why it is essential for recruiters to have an effective hiring strategy in place to find the right talent. As the first step of the process, recruiters must administer a scientifically validated skills assessment to screen and shortlist candidates. Based on the test results, candidates that seem most suited for the job opening should be invited for an interview. Beginning with basic questions about their experience, career, education, etc., recruiters can then move on to the scenario-based SQL interview questions and answers.

Mercer | Mettl offers a range of pre-employment assessment tests that have been developed by subject matter experts to help recruiters successfully find top talent for their organization. Mercer | Mettl’s pre-employment SQL DBA test can measure the fundamental knowledge candidates have in the basics of the SQL server as well as their hands-on proficiency and expertise. The SQL DBA test can be used to objectively screen candidates and identify the most suitable hires.