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Advanced 20 min readModule: Module 8: Window Functions (ROW_NUMBER, RANK, LEAD, LAG)

Window Functions (ROW_NUMBER, RANK, LEAD, LAG)

Perform advanced calculations across rows without collapsing them with the OVER (PARTITION BY) clause.

What You Will Learn in This Lesson

  • Difference between GROUP BY (collapses rows) and Window functions (retains rows)
  • Ranking rows with ROW_NUMBER(), RANK(), and DENSE_RANK()
  • Comparing against previous/next rows with LAG() and LEAD()

Introduction & Core Concept

A window function performs a calculation across a set of table rows that are somehow related to the current row, without collapsing the individual rows into a single summary output.
WHY DOES THIS MATTER IN THE REAL WORLD?

Calculating running totals or month-over-month growth takes 1 line with window functions instead of 5 complex self-joins.

Top 3 Products per Category with ROW_NUMBER

sql
sql
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WITH RankedProducts AS (
    SELECT 
        product_name,
        category,
        price,
        ROW_NUMBER() OVER (PARTITION BY category ORDER BY price DESC) as rank_in_category
    FROM products
)
SELECT product_name, category, price
FROM RankedProducts
WHERE rank_in_category <= 3;

Line-by-Line Technical Breakdown

1LEAD(sales, 1) OVER (ORDER BY month) retrieves the next month's sales value.

Try It Yourself (Interactive Editor)

Modify the code in real-time and click Run to test live browser output and console logs.

Intelligent Code Runner & Live Sandbox[SQL]
SQL SOURCE EDITOR
Interactive Live Code

Industry Best Practices & Professional Standards

  • Use window functions for ranking, pagination, and time-series delta analysis.

Lesson Summary & Core Takeaways

  • Window functions unlock advanced analytics without procedural code.