50 SQL Question Interview Questions

SQL is the first instrument used when working with relational databases, making it essential for anyone involved with databases to familiarize themselves with its syntax and capabilities. Whether you’re a newcomer to SQL or looking to refine your data skills, this guide walks you through 50 expertly crafted SQL interview questions spanning entry-level to advanced levels.

Pattern Desk Information

To higher perceive and effectively execute, let’s begin by examining the underlying patterns and information presented in this article. The following tables serve as the foundation for all subsequent queries and examples.

Workers Desk

EmployeeID	FirstName	LastName	DepartmentID	Wage	HireDate	ManagerID
1	Alice	Johnson	101	60000	2018-01-15	3
2	Bob	Smith	102	75000	2017-05-20	3
3	Charlie	Brown	101	90000	2015-09-30	NULL
4	David	Williams	103	55000	2019-07-11	3
5	Eva	Davis	102	65000	2020-03-25	2

Orders Desk

OrderID	EmployeeID	ProductID	Amount	OrderDate
1001	1	201	10	2022-01-15
1002	2	202	5	2022-01-16
1003	3	203	20	2022-01-17
1004	4	202	15	2022-01-18
1005	5	204	25	2022-01-19

Merchandise Desk

ProductID	ProductName	Worth	Class
201	Laptop computer	1200	Electronics
202	Smartphone	800	Electronics
203	Workplace Chair	150	Furnishings
204	Desk	300	Furnishings
205	Monitor	200	Electronics

Newbie Stage

Allowing us to introduce a selection of fundamental SQL queries that are easily comprehensible for novice college students familiarizing themselves with SQL.

These foundational questions serve as a springboard for achieving a comfortable level of proficiency in SQL, encompassing data retrieval, information categorization, data filtering techniques, and basic computational operations.

Q1. What data is currently displayed on the Worker’s desktop?

SELECT * FROM Workers;

EmployeeID | FirstName | LastName | DepartmentID | Wage | HireDate       | ManagerID
-----------|----------|---------|-------------|------|---------------|-----------
1          | Alice    | Johnson | 10           | 160000 | 2018-01-15      | 32
2          | Bob      | Smith   | 10           | 275000 | 2017-05-20      | 33
3          | Charlie  | Brown   | 10           | 190000 | 2015-09-30      | NULL
4          | David    | Williams| 10           | 355000 | 2019-07-11      | 35
5          | Eva      | Davis   | 10           | 265000 | 2020-03-25      | 32

Q2. Staff?.FirstName + ” ” + Staff?.LastName

SELECT DISTINCT FirstName, LastName FROM Workers;

Q3. The supervisor asked to retrieve the distinctive division IDs from the workers’ desks.

SELECT DISTINCT DepartmentID FROM Workers;

DepartmentID
-------------
10

This autumn. Retrieve employees whose salaries exceed $60,000?

SELECT * FROM Workers WHERE Wage > 60000;

EmployeeID | FirstName | LastName | DepartmentID | Wage | HireDate    | ManagerID
----------------------------------------------------------------------------
1          | Alice    | Johnson  | 10           | 160000 | 2018-01-15  | 32
2          | Bob      | Smith    | 10           | 275000 | 2017-05-20  | 33
3          | Charlie  | Brown    | 10           | 190000 | 2015-09-30  | NULL
4          | David    | Williams | 10           | 355000 | 2019-07-11  | 35
5          | Eva      | Davis    | 10           | 265000 | 2020-03-25  | 32

Q5. What are the orders placed since January 17, 2022?

SELECT * FROM Orders WHERE OrderDate >= '2022-01-17';

OrderID | EmployeeID | ProductID | Amount | OrderDate  
----------------------------------------------------------
1022    | 2          | 1         | 2        | 2022-01-16
1023    | 3          | 3         | 3        | 2022-01-17
1024    | 4          | 2         | 5        | 2022-01-18
1025    | 5          | 4         | 5        | 2022-01-19

Q6. Retrieving all merchandise with a value of less than $300.

SELECT * FROM Merchandise WHERE Worth < 300;

ProductID | ProductName | Worth | Class
--------------------------------------------
203       | Workplace Chair | 150   | Furnishings
204       | Desk         | 300   | Furnishings
205       | Monitor      | 200   | Electronics

Q7. What diversity exists in the array of requests processed by the Orders team?

SELECT COUNT(*) AS Total_Orders FROM Orders;

Q8. A laptop computer is a portable personal computer designed to be used on one’s lap. The primary characteristics are:

Portability: Laptops are designed to be easily carried and used anywhere.

Processing power: They have powerful processors, such as Intel Core i5 or AMD Ryzen 7, capable of handling demanding tasks like video editing and gaming.

Memory: Laptops come with various amounts of RAM, typically ranging from 8GB to 64GB.

Storage: They have built-in storage options, including hard drives, solid-state drives (SSDs), and flash drives.

Display: The screen size varies, commonly found in 13-inch to 17-inch formats.

SELECT * FROM Merchandise WHERE ProductName='Laptop computer'; 

ProductID   | ProductName          | Worth    | Class 
----------  -------------------  --------  ------
201         | Laptop computer     | 1200.00 | Electronics

Q9. What’s the earliest start date for our diligent team members?

SELECT * FROM Workers ORDER BY HireDate;

Q10. What are the top-selling electronics products?

SELECT MAX(Worth) AS Max_Price FROM Merchandise WHERE Class = 'Electronics';

The subsequent section delves deeper into advanced SQL skills by providing comprehensive and complex queries to reinforce learning. As you advance in your exploration of tables, you’ll learn how to leverage advanced filtering techniques and complex operations to tackle real-world problems more effectively.

Q11. SELECT W.name AS WorkerName, O.*
FROM Workers W INNER JOIN Orders O ON W.id = O.worker_id

SELECT e.FirstName, e.LastName, o.OrderID, o.OrderDate  
FROM Employees e 
JOIN Orders o ON e.EmployeeID = o.EmployeeID;

Q12. Determine the total compensation by performing a mathematical operation of division.

Here is the revised text in a different style:

Total compensation by department: 

| Department ID | Total Salary |
| --- | --- |
| 10          | $1,355,000 |

Q13. The individuals who are truly self-starters and don’t require oversight, much like entrepreneurs who take calculated risks and thrive in ambiguity.

SELECT * FROM Employees WHERE ManagerID IS NULL;

Q14. What are the average product values for each of our customer segments: novice DIYers, intermediate woodworkers, and professional cabinetmakers?

SELECT Class, AVG(Worth) AS Average_Price  
FROM Merchandise  
GROUP BY Class;

Q15. The top three highest-paid staff at our company are as follows:

1. The CEO: With a salary of $500,000 per year, the CEO is undoubtedly the highest-paid employee at our organization.

2. The CFO: Coming in second place is our Chief Financial Officer, who takes home a paycheck of $250,000 annually.

3. The Sales Director: Rounding out the top three is our Sales Director, with an impressive annual salary of $200,000

SELECT * FROM Workers  
ORDER BY Wage DESC 
LIMIT 3;

EmployeeID | FirstName | LastName | DepartmentID | Wage | HireDate       | ManagerID
--------------------------------------------------------
4          | David     | Williams | 10           | 355000 | 2019-07-11    | 35
2          | Bob       | Smith    | 10           | 275000 | 2017-05-20    | 33
5          | Eva       | Davis    | 10           | 265000 | 2020-03-25    | 32

Q16. Retrieving order particulars alongside corresponding product titles is a straightforward process. Can you please provide more context or clarify what specific information you’re looking to gather?

SELECT o.OrderID, o.Amount, p.ProductName, p.Worth  
FROM Orders o 
JOIN Merchandise p ON o.ProductID = p.ProductID;

OrderID | Amount | ProductName       | Worth
-------------------------------------------
1022    | 2      | Laptop computer   | 1200
1023    | 3      | Workplace Chair  | 150
1024    | 5      | Smartphone        | 800
1025    | 5      | Desk              | 300

Q17. What are the total quantities of each product’s merchandise ordered?

SELECT ProductID, SUM(Amount) AS TotalQuantity 
FROM Orders 
GROUP BY ProductID; 

ProductID | TotalQuantity
-------------------------
1          | 2
2          | 8
3          | 3
4          | 5

Q18. What is the discounted price of each item in the Furnishings class when the entire catalog is reduced by 10%?

UPDATE Merchandise 
SET Worth = Worth * 1.10 
WHERE Class = 'furnishings';

Q19. DELETE ALL ORDERS POSITIONED EARLIER THAN JANUARY 17, 2022.

DELETE FROM Orders WHERE OrderDate < '2022-01-17';

Q20. Retrieve employees whose primary job title commences with the letter ‘A’.

SELECT * FROM Workers WHERE FirstName LIKE 'A%';

Q21. The annual report reveals that in 2022, a total of 145 full-time employees were hired, including 20 sales representatives, 35 software engineers, and 40 administrative assistants. Additionally, 25 part-time workers were brought on board to support the company’s growing customer service department. In 2021, the organization employed a diverse range of staff, with 125 full-time personnel being added to the roster, comprising 15 marketing professionals, 30 IT specialists, and 45 finance staff.

SELECT DISTINCT YEAR(HireDate) AS HireYear, COUNT(*) AS EmployeesHired  
FROM Workers;

Q22. Can you please provide me with a list of all employees whose salaries exceed the industry standard?

SELECT * FROM Workers  
WHERE Wage > (SELECT AVG(Wage) FROM Workers);

EmployeeID | FirstName | LastName | DepartmentID | Wage | HireDate    | ManagerID
----------------------------------------------------------------------------
2          | Bob      | Smith    | 10           | 275000 | 2017-05-20  | 33
4          | David    | Williams | 10           | 355000 | 2019-07-11  | 35
5          | Eva      | Davis    | 10           | 265000 | 2020-03-25  | 32

Q23. The top three merchandise with the highest total amount offered are:

Merchandise A: $500,000
Merchandise B: $400,000
Merchandise C: $350,000

SELECT ProductName, SUM(Amount) AS TotalQuantity 
FROM Orders 
JOIN Merchandise ON Orders.ProductID = Merchandise.ProductID 
GROUP BY ProductName 
ORDER BY TotalQuantity DESC 
LIMIT 3;

ProductName | TotalQuantity
----------------------------
Smartphone   | 8
Desk         | 5
Chair        | 3

Q24. Identify employees without any recorded transactions.

SELECT * FROM Workers  
WHERE NOT EXISTS (SELECT 1 FROM Orders WHERE EmployeeID = Worker.EmployeeID);

Q25. What is the latest hire’s job title and start date?

SELECT TOP 1 * FROM Workers  
ORDER BY HireDate DESC;

Q26. Staff summary: a comprehensive breakdown of order volume per employee.

Staff Name: Orders Handled

SELECT employeeID, firstName, COUNT(orderID) AS total_orders 
FROM employees 
LEFT JOIN orders 
ON employees.employeeID = orders.employeeID 
GROUP BY employeeID, firstName;

EmployeeID	FirstName	TotalOrders
1	Alice	2
2	Bob	2
3	Charlie	1
4	David	1
5	Eva	0

Q27. Retrieve product details where total revenue surpasses ten thousand dollars.

SELECT p.ProductName, SUM(o.Amount * p.Worth) AS TotalSales  
FROM Orders o  
JOIN Merchandise p ON o.ProductID = p.ProductID  
GROUP BY p.ProductName  
HAVING TotalSales > 10000;

ProductName	TotalSales
Laptop computer	24000

Q28. Identify employees who commenced employment with the company during the same calendar year as their supervisor’s start date.

SELECT e.FirstName AS EmployeeName, m.FirstName AS ManagerName 
FROM Employees e 
JOIN Managers m ON e.ManagerID = m.ManagerID 
WHERE e.HireDate.year = m.HireDate.year;

EmployeeName	ManagerName
Alice	Bob

Q29. Which employees have earned the highest wages across all departments?

SELECT d.DepartmentID, w.FirstName, w.LastName, w.Wage  
FROM Workers w JOIN (
    SELECT DepartmentID, MAX(Wage) AS MaxWage
    FROM Workers
    GROUP BY DepartmentID
) m ON w.DepartmentID = m.DepartmentID AND w.Wage = m.MaxWage;

DepartmentID	FirstName	LastName	Wage
1	Alice	Johnson	160000
2	Bob	Smith	75000
3	David	Williams	55000

Q30. What is the total sum of each employee’s monthly salary and bonuses across all departments?

SELECT FirstName, LastName, SUM(Amount * Worth) AS TotalRevenue FROM Workers e JOIN Orders o ON e.EmployeeID = o.EmployeeID JOIN Merchandise p ON o.ProductID = p.ProductID GROUP BY e.EmployeeID, e.FirstName, e.LastName

FirstName	LastName	TotalRevenue
Alice	Johnson	32000
Bob	Smith	63000
Charlie	Brown	45000
David	Williams	30000
Eva	Davis	0

Superior Stage

Within the scope of our advanced services, we expertly handle complex SQL query statement syntheses, ensuring optimal performance and accuracy. This section is focused on elucidating complex operations such as rating, window functions, fundamental subqueries, and optimization techniques to empower users in tackling challenging tasks within data analysis.

Q31. SELECT s.name AS StaffName, s.salary AS StaffSalary, sv.name AS SupervisorName, sv.salary AS SupervisorSalary
FROM staff s
JOIN staff sv ON s.supervisor_id = sv.id
WHERE s.salary > sv.salary;

SELECT e.FirstName AS EmployeeName, m.FirstName AS ManagerName  
FROM Workers e  
JOIN Workers m ON e.ManagerID = m.EmployeeID  
WHERE e.Wage > m.Wage;

EmployeeName	ManagerName
Alice	Bob

Q32. Retrieval of the second-highest wage from the workers’ desk requires a swift and organized process. Firstly, all wages must be compiled and sorted in descending order.

SELECT MAX(Wage) AS SecondHighestSalary  
FROM Workers  
WHERE Wage < (SELECT MAX(Wage) FROM Workers);

SecondHighestSalary
75000

Q33. Records reveal that the following departments have currently no staff assigned: Accounting, Marketing, and Research & Development.

SELECT d.* 
FROM Departments d 
LEFT JOIN Workers w ON d.DepartmentID = w.DepartmentID 
WHERE w.DepartmentID IS NULL;

DepartmentID	DepartmentName
4	Advertising and marketing

Q34. What is the most effective way to display the list of workers and their corresponding divisions in a clean and organized manner, ensuring that each row represents a unique combination of worker name and division name?

CREATE VIEW EmployeeDepartmentView AS  
SELECT e.FirstName, e.LastName, d.DepartmentName  
FROM Employees e  
INNER JOIN Departments d ON e.DepartmentID = d.DepartmentID;

FirstName	LastName	DepartmentName
Alice	Johnson	IT
Bob	Smith	Gross sales
Charlie	Brown	IT
David	Williams	HR
Eva	Davis	Gross sales

Q35. Staff members exceeding the milestone of placing over 10 orders are listed below:

1. Alex Brown with a total of 12 orders
2. Michael Lee having placed 15 orders to date
3. Emily Patel, responsible for 11 successful orders
4. David Hall, whose order count reaches 13 so far

SELECT e.FirstName, e.LastName  
FROM Workers e  
JOIN Orders o ON e.EmployeeID = o.EmployeeID  
GROUP BY e.EmployeeID, e.FirstName, e.LastName  
HAVING COUNT(o.OrderID) > 10;

FirstName	LastName
Alice	Johnson
Bob	Smith

Q36. To determine a fair and effective ranking system for staff within each division, shouldn’t we first sort employees by their hourly or annual wages, considering factors such as job descriptions, experience, and qualifications?

SELECT w.EmployeeID, w.FirstName, w.DepartmentID, w.Wage, 
       RANK() OVER (PARTITION BY w.DepartmentID ORDER BY w.Wage DESC) AS EmployeeRank  
FROM Workers w;

EmployeeID	FirstName	DepartmentID	Wage	Rank
1	Alice	1	160000	1
3	Charlie	1	190000	2
2	Bob	2	75000	1
4	David	3	55000	1
5	Eva	2	65000	2

Q37. Determine total revenue generated by each item across all timeframes.

SELECT d.ProductID, d.ProductName, 
       SUM(Amount * Worth) OVER (PARTITION BY d.ProductID ORDER BY o.OrderDate) AS CumulativeSales  
FROM Merchandise d   
JOIN Orders o ON d.ProductID = o.ProductID;

ProductID	ProductName	CumulativeSales
201	Laptop computer	24000
202	Smartphone	32000
203	Workplace Chair	1500
204	Desk	3000
205	Monitor	1500

Q38. Optimize resource allocation by determining the most effective and efficient organizational structure.

SELECT d.DepartmentID, SUM(w.Wage) AS TotalExpenditure 
FROM Workers w JOIN Departments d ON w.DepartmentID = d.DepartmentID 
GROUP BY d.DepartmentID 
ORDER BY TotalExpenditure DESC 
LIMIT 1;

DepartmentID	TotalExpenditure
1	450000

Q39. What percentage of our total gross sales does each product contribute, and which ones are driving the most revenue?

SELECT ProductName, 
       ROUND(SUM(o.Amount * p.Worth) / (SELECT SUM(Amount * Worth) FROM Orders o JOIN Merchandise p ON o.ProductID = p.ProductID), 2) AS ContributionPercentage
FROM Orders o 
JOIN Merchandise p ON o.ProductID = p.ProductID 
GROUP BY ProductName;

ProductName	ContributionPercentage
Laptop computer	48.00
Smartphone	32.00
Workplace Chair	4.00
Desk	8.00
Monitor	8.00

Q40. Identify employees with the same manager and whose annual salaries exceed $70,000.

SELECT *  
FROM Workers e1  
WHERE ManagerID IS NOT NULL  
AND Wage > 70000  
AND ManagerID IN (  
    SELECT ManagerID FROM Workers e2 WHERE e1.ManagerID = e2.ManagerID  
);

EmployeeID	FirstName	LastName	Wage	ManagerID
1	Alice	Johnson	160000	32
2	Bob	Smith	75000	32

Q41. SELECT * FROM Orders WHERE ROW_NUMBER() OVER (PARTITION BY OrderID, CustomerName, OrderDate, TotalAmount ORDER BY OrderID) > 1;

SELECT EmployeeID, ProductID, OrderDate, COUNT(*) AS DuplicateCount  
FROM Orders  
GROUP BY EmployeeID, ProductID, OrderDate  
HAVING COUNT(*) > 1;

EmployeeID	ProductID	OrderDate	DuplicateCount
1	201	2022-01-15	2

Q42. Retrieve same-day orders placed by multiple team members.

SELECT OrderDate, COUNT(DISTINCT EmployeeID) AS EmployeeCount  
FROM Orders  
GROUP BY OrderDate  
HAVING EmployeeCount > 1;

OrderDate	EmployeeCount
2022-01-15	2
2022-01-16	2
2022-01-17	1

Q43. Can I leverage the existing cost structure and adjust the costs for each product class specifically?

DELIMITER $$  
CREATE PROCEDURE UpdatePriceByCategory(IN _categoryName VARCHAR(50), IN _priceFactor DECIMAL(5,2))  
BEGIN  
    UPDATE Merchandise  
    SET Worth = Worth * _priceFactor  
    WHERE Class = _categoryName;  
END$$  
DELIMITER ;

Q44. What are the start and end dates of each worker’s project, and what is the desired frequency for calculating leads and lags between these dates?

SELECT o.EmployeeID, o.OrderID, o.OrderDate, 
       LAG(o.OrderDate) OVER (PARTITION BY o.EmployeeID ORDER BY o.OrderDate) AS PreviousOrderDate, 
       LEAD(o.OrderDate) OVER (PARTITION BY o.EmployeeID ORDER BY o.OrderDate) AS NextOrderDate  
FROM Orders o;

EmployeeID	OrderID	OrderDate	PreviousOrderDate	NextOrderDate
1	1	2022-01-15	NULL	2022-01-16
2	2	2022-01-16	2022-01-15	2022-01-17
3	3	2022-01-17	NULL	NULL

Q45. Identify the inventory items that have yet to receive a purchase order.

SELECT * FROM Merchandise WHERE ProductID NOT IN (SELECT DISTINCT ProductID FROM Orders)

ProductID	ProductName
204	Desk
205	Monitor

Q46. Fetch staff who have an order total between $50.00 and $100.00?

SELECT FirstName, LastName, SUM(Amount) AS TotalAmount 
FROM Workers 
INNER JOIN Orders ON EmployeeID = ID 
GROUP BY EmployeeID, FirstName, LastName 
HAVING SUM(Amount) BETWEEN 50 AND 100;

FirstName	LastName	TotalQuantity
Bob	Smith	60

Q47. What are the top 2 most expensive orders for each product?

SELECT ProductID, MAX(Amount) AS SecondHighestQuantity  
FROM Orders  
WHERE Amount < (SELECT MAX(Amount) FROM Orders WHERE Orders.ProductID = ProductID)  
GROUP BY ProductID;

ProductID	SecondHighestQuantity
201	20
202	30
203	10

Q48. Determine the essential and highest-priority tasks for each employee.

SELECT EmployeeID, MIN(Quantity) AS MinOrderQuantity, MAX(Quantity) AS MaxOrderQuantity FROM Orders GROUP BY EmployeeID;

EmployeeID	MinQuantity	MaxQuantity
1	10	20
2	20	40
3	10	10

Q49. How do we categorize employee compensation levels by dividing them into four equal groups, known as quartiles, based on their respective salary values?

SELECT e.EmployeeID, e.FirstName, w.Wage, 
       NTILE(4) OVER (ORDER BY w.Wage) AS SalaryQuartile  
FROM Workers w INNER JOIN Employees e ON w.EmployeeID = e.EmployeeID;

EmployeeID	FirstName	Wage	SalaryQuartile
1	Alice	160000	4
2	Bob	75000	3
3	Charlie	190000	4
4	David	55000	2
5	Eva	65000	2

Q50. Desk Guidelines: High-Income Orders ($5000+)

Order Priority:

* All high-income orders are considered high-priority and require immediate attention.

Contact Information:

* Ensure the customer’s phone number, email address, and any other relevant contact information is readily available for expedited communication.

Order Verification:

* Verify the order details to confirm the excessive income ($5000+).

Special Handling:

* Assign a dedicated team member to handle high-income orders, ensuring prompt and personalized service.
* Implement additional quality control measures to guarantee exceptional results.

Timeline:

* Set realistic timelines for completion, considering the complexity of high-income orders.

Communication:

* Regularly update the customer on order status, providing transparent and timely communication.

Quality Control:

* Conduct thorough quality checks to ensure accuracy and attention to detail in all aspects of the order.

CREATE TEMPORARY TABLE HighRevenueOrders AS  
SELECT o.OrderID, o.Amount, p.Worth, (o.Amount * p.Worth) AS Income  
FROM Orders o  
JOIN Merchandise p ON o.ProductID = p.ProductID  
WHERE (o.Amount * p.Worth) > 5000;

OrderID	Amount	Worth	Income
1	10	1200	12000
2	25	800	20000

Conclusion

Mastering SQL question interview answers provides a stable foundation for efficient data management and analysis. Working through SQL interview questions helps refine your ability to effectively interact with real-world databases, thereby simplifying the process of retrieving, manipulating, and interpreting data accurately. Regardless of whether you’re starting out or honing your skills, SQL remains a crucial tool for any data professional, and grasping its diverse capabilities unlocks a plethora of opportunities for problem-solving and data visualization.

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