Beginner

613. JOIN with Window Function

Combine JOINs with window functions to perform advanced analysis without collapsing detail rows.

📘 Lesson 613 of 728 ⏱ 15 min 🎯 Advanced

Window functions calculate values across related rows while keeping individual records visible. They can be applied to data after JOINing multiple tables.

This combination is useful when detailed transaction information and analytical calculations are needed together.

Show each order along with the customer's total order value.

SQL 
SELECT
    c.CustomerName,
    o.OrderID,
    o.OrderAmount,
    SUM(o.OrderAmount) OVER (
        PARTITION BY o.CustomerID
    ) AS CustomerTotal
FROM Customers c
INNER JOIN Orders o
    ON c.CustomerID = o.CustomerID;

Used in customer analytics, sales ranking, financial analysis, and advanced reporting.

  • JOIN combines related tables.
  • Window functions preserve individual rows.
  • PARTITION BY defines the analytical group.
  • Aggregates can be used as window functions.
  • Useful for detail plus summary reporting.
Why use a window function after a JOIN?

It allows calculations across related rows while still keeping the detailed JOINed records.

How does PARTITION BY help here?

It defines the group of rows over which the window calculation is performed.

Have you finished this lesson?

Introduction to SQL – All Lessons