06 SQL Interview Guide: Cumulative Sum for Each Employee | Must-Know SQL Interview Question.

Boost Your SQL Skills with This Powerful Query!

One of the most frequently asked SQL interview questions is:
💡 "How do you calculate the cumulative sum for each employee?"

In this video, we’ll break it down step by step and explain:
✔️ How to use the SUM() window function to calculate cumulative totals
✔️ How PARTITION BY ensures the sum is calculated per employee
✔️ The difference between window functions and aggregate functions
✔️ Real-world applications of cumulative sums in payroll, sales tracking, and analytics

You can try this query also for cumulative salary:
SELECT
EmployeeID,
FirstName,
LastName,
Salary,
SUM(Salary) OVER (PARTITION BY EmployeeID ORDER BY JoinDate) AS CumulativeSalary
FROM Employees;
By the end of this tutorial, you’ll not only write the SQL query confidently but also understand how it works and why it’s useful in real-life scenarios.

🎯 Who is this video for?
✅ Data Analysts preparing for SQL interviews
✅ Data Scientists looking to enhance their SQL knowledge
✅ SQL Developers who want hands-on experience with window functions

🔹 Real-World Example:
Imagine you work in HR, and your manager wants to see the total earnings of each employee over time. Instead of manually summing up salaries, SQL lets you calculate cumulative sums instantly!

💡 Pro Tip: The SUM() OVER() function is widely used in finance, sales reporting, and data analytics—so mastering it can give you an edge in your next SQL interview!

📢 Want More SQL Interview Prep? Check out our full SQL playlist 📌 for expert guidance!

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Видео 06 SQL Interview Guide: Cumulative Sum for Each Employee | Must-Know SQL Interview Question. канала The Data Mentor