SQL Practice Questions and Interview Examples

This guide provides hands-on SQL exercises and interview-style questions using real-world dataset formats. Perfect for students, job seekers, and data enthusiasts.

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Sample Dataset: Employees Table

+----+--------+-----------+------------+---------+
| ID | Name   | Dept      | Salary     | Joining |
+----+--------+-----------+------------+---------+
| 1  | Alice  | HR        | 50000      | 2019-05 |
| 2  | Bob    | IT        | 75000      | 2020-01 |
| 3  | Carol  | Finance   | 68000      | 2018-09 |
| 4  | Dave   | IT        | 80000      | 2021-03 |
| 5  | Eve    | Finance   | 70000      | 2020-07 |
+----+--------+-----------+------------+---------+
    

1. Basic Practice Questions

Q1. Select all employees in the IT department

SELECT * FROM employees WHERE dept = 'IT';

Q2. Find total salary paid to the Finance department

SELECT SUM(salary) FROM employees WHERE dept = 'Finance';

Q3. Count employees who joined after 2019

SELECT COUNT(*) FROM employees WHERE joining > '2019-12-31';

Q4. List employee names ordered by salary descending

SELECT name FROM employees ORDER BY salary DESC;

Q5. Find average salary by department

SELECT dept, AVG(salary) AS avg_salary FROM employees GROUP BY dept;

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2. Intermediate SQL Exercises

Q6. Display the highest-paid employee in each department

SELECT dept, name, salary
FROM employees e
WHERE salary = (
  SELECT MAX(salary)
  FROM employees
  WHERE dept = e.dept
);
    

Q7. Retrieve employees whose name starts with 'A'

SELECT * FROM employees WHERE name LIKE 'A%';

Q8. Add a new employee

INSERT INTO employees (ID, Name, Dept, Salary, Joining)
VALUES (6, 'Frank', 'HR', 55000, '2023-02');
    

Q9. Update salary of Bob by 10%

UPDATE employees
SET salary = salary * 1.10
WHERE name = 'Bob';
    

Q10. Delete employees from the HR department

DELETE FROM employees WHERE dept = 'HR';

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3. Interview-Style SQL Questions

Q11. What is the difference between WHERE and HAVING?

WHERE filters rows before grouping; HAVING filters after aggregation.

Q12. Retrieve departments having more than 1 employee

SELECT dept, COUNT(*) AS emp_count
FROM employees
GROUP BY dept
HAVING COUNT(*) > 1;
    

Q13. Write a query to rank employees by salary in each department

SELECT name, dept, salary,
  RANK() OVER (PARTITION BY dept ORDER BY salary DESC) AS rank
FROM employees;
    

Q14. Explain use of JOIN in multi-table queries?

JOIN is used to combine rows from multiple tables based on related columns (e.g., foreign keys).

Q15. What is the purpose of indexing?

Indexes speed up data retrieval by reducing the number of rows scanned.

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Also Read:

• SQL Clauses and Operators
• SQL Joins and Subqueries
• SQL Constraints, Indexes, and Views

Final Tips

• Practice regularly using mock datasets.
• Use platforms like LeetCode, Hackerrank, or SQLZoo for timed challenges.
• Understand logic, not just syntax.

For more tutorials, visit Sabbir93s SQL Series.