Module 6: Window Functions

Window Functions are often called the “Game Changer” of SQL. They allow you to perform advanced analytical calculations (like running totals, rankings, and year-over-year comparisons) while keeping the individual row-level detail of your data.

Before Window Functions, these tasks required extremely complex and slow self-joins or subqueries.

Learning Objectives

In this module, you will:

• Understand the anatomy of the OVER() clause.
• Master ranking functions: ROW_NUMBER, RANK, and DENSE_RANK.
• Perform time-series analysis using LEAD and LAG.
• Calculate running totals and moving averages.
• Control the scope of your calculations using Window Frames (ROWS BETWEEN).

Chapters

6.1 Window Anatomy Understanding OVER(), PARTITION BY, and ORDER BY.

6.2 Ranking Functions ROW_NUMBER, RANK, DENSE_RANK, and NTILE.

6.3 Value Extraction Looking ahead and behind with LEAD and LAG.

6.4 Window Aggregates Running totals and moving averages.

6.5 Window Frames The power of ROWS BETWEEN for rolling windows.

Tip

A Window Function never reduces the number of rows in your result set. This is the key difference between a Window Function and a standard GROUP BY aggregate.