Interview Bite

If you’re preparing for a technical interview, having a solid grasp of basic SQL won’t be enough. Most mid to senior-level interviews test your ability to solve complex SQL queries that involve multiple tables, subqueries, joins, aggregates, and logic.

In this article, we’ll walk through real-world complex SQL queries for interview preparation that will not only sharpen your database skills but also give you an edge during interviews.

---

📌 Why You Need to Learn Complex SQL Queries for Interviews

Interviewers use SQL to assess:

• Your ability to understand and manipulate large datasets
• Logical thinking and problem-solving ability
• Proficiency in joins, subqueries, window functions, and aggregations
• Real-world data analytics scenarios

That’s why complex SQL queries for interview preparation are a must in your study checklist.

---

📊 Sample Database Structure

Let’s assume the following tables:

Employees

emp_id	emp_name	dept_id	salary	join_date
1	Alice	101	60000	2020-01-10
2	Bob	102	55000	2021-06-12
3	Carol	101	70000	2019-03-04
4	Dave	103	65000	2022-09-15
5	Emma	102	58000	2020-11-28

Departments

dept_id	dept_name
101	HR
102	IT
103	Finance

---

🔥 Top 10 Complex SQL Queries for Interview Preparation

1. Find the highest-paid employee in each department.

SELECT e.emp_name, e.salary, d.dept_name
FROM Employees e
JOIN Departments d ON e.dept_id = d.dept_id
WHERE salary IN (
  SELECT MAX(salary)
  FROM Employees
  GROUP BY dept_id
);

---

2. List employees who earn more than the average salary of their department.

SELECT e.emp_name, e.salary, d.dept_name
FROM Employees e
JOIN Departments d ON e.dept_id = d.dept_id
WHERE e.salary > (
  SELECT AVG(salary)
  FROM Employees
  WHERE dept_id = e.dept_id
);

---

3. Find departments with more than 1 employee.

SELECT dept_id, COUNT(*) AS emp_count
FROM Employees
GROUP BY dept_id
HAVING COUNT(*) > 1;

---

4. Get the second highest salary from the Employees table.

SELECT MAX(salary) AS second_highest
FROM Employees
WHERE salary < (
  SELECT MAX(salary) FROM Employees
);

---

5. List employees who joined in the last 12 months.

SELECT * FROM Employees
WHERE join_date >= DATE_SUB(CURDATE(), INTERVAL 1 YEAR);

---

6. Show employee name and department name for all employees.

SELECT e.emp_name, d.dept_name
FROM Employees e
LEFT JOIN Departments d ON e.dept_id = d.dept_id;

---

7. Find duplicate salaries.

SELECT salary, COUNT(*) 
FROM Employees
GROUP BY salary
HAVING COUNT(*) > 1;

---

8. List employees with the same salary as another employee.

SELECT emp_name, salary
FROM Employees
WHERE salary IN (
  SELECT salary
  FROM Employees
  GROUP BY salary
  HAVING COUNT(*) > 1
);

---

9. Rank employees by salary within each department.

SELECT emp_name, dept_id, salary,
       RANK() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS dept_rank
FROM Employees;

---

10. Show total salary expense for each department.

SELECT d.dept_name, SUM(e.salary) AS total_expense
FROM Employees e
JOIN Departments d ON e.dept_id = d.dept_id
GROUP BY d.dept_name;

---

🎯 Tips for Mastering Complex SQL Queries

• Understand the business logic before jumping to code
• Break down the query into smaller subqueries
• Use CTEs (WITH clause) to simplify readability
• Always double-check JOIN conditions
• Practice on real datasets (Kaggle, LeetCode, etc.)

---

🙋 Frequently Asked Questions (FAQs)

Q1. What is considered a complex SQL query?

A complex query involves multiple tables, nested subqueries, aggregate functions, or analytical functions.

Q2. How can I improve my SQL for interviews?

Practice 1–2 queries daily, review interview questions, and use platforms like LeetCode, Hackerrank, or Mode SQL.

Q3. Is SQL enough to get a job in data?

Yes, SQL is a core requirement for data analysts, BI developers, and even data scientists.

---

💬 Final Words

Practicing complex SQL queries for interview preparation helps you build logical thinking, database fluency, and confidence for real interviews.

Start from these examples, tweak them, and build your own logic. Mastering SQL is one step closer to acing your dream job!