Calculating Running Totals with SQL

Welcome to **Day 65**. Today we build the "Cumulative Chart." How much have we earned *total* since the beginning of the year?

The Running Total Logic

Normally, `SUM()` gives you the total of all rows. But inside a window, if you add an `ORDER BY`, it becomes a **cumulative sum**.

SELECT

month,

revenue,

SUM(revenue) OVER(ORDER BY month) as running_total

FROM monthly_sales;

The `ORDER BY` inside the `OVER` clause tells SQL: "For this row, sum all rows from the beginning of the list up to the current row."

You can even track running totals *per customer*:

SELECT

customer_id,

order_date,

amount,

SUM(amount) OVER(PARTITION BY customer_id ORDER BY order_date) as customer_cumulative_spend

FROM orders;

This is how fintech apps calculate your "Balance History" chart!

Calculate the cumulative count of new signups per day for the last month.

*Day 66: Moving Averages (The Secret to Smooth Charts).*