How to Calculate Cumulative Sum/Running Total in SQL Server

The concept of a cumulative sum or running total is quite useful in many reporting and analytical scenarios. It allows you to see a progressive sum of values as they appear in a data set.

In SQL Server, calculating a cumulative sum can be easily achieved using window functions, specifically the SUM() function with the OVER() clause. Let's explore how to do it step by step.

Basic Syntax

To calculate a running total, you can use the following query:

SELECT column_name,
   SUM(column_name) OVER (ORDER BY column_name) AS running_total
FROM table_name;

Example: Sales Data

Let's say we have a table called Sales with the following columns:

• SaleDate - The date the sale was made
• Amount - The amount of the sale

Here’s how you can calculate a running total of the Amount column, ordered by the SaleDate:

SELECT SaleDate, 
   Amount, 
   SUM(Amount) OVER (ORDER BY SaleDate) AS RunningTotal
FROM Sales;

This query will return the SaleDate, the Amount of each sale, and a running total of the Amount ordered by the SaleDate.

Partitioning the Data

If you need to calculate the running total for different groups of data, such as by ProductID or StoreLocation, you can use the PARTITION BY clause within the OVER() function.

Here’s an example where we calculate the running total for each product:

SELECT ProductID, 
   SaleDate, 
   Amount, 
   SUM(Amount) OVER (PARTITION BY ProductID ORDER BY SaleDate) AS RunningTotal
FROM Sales;

This query will calculate a running total of Amount for each ProductID, ordered by SaleDate.

Conclusion

Calculating a cumulative sum or running total in SQL Server is simple and efficient using window functions. You can use the SUM() function with OVER() to calculate a running total across a set of data, optionally partitioned by a group.

This technique is essential for reporting and analysis, providing insights into cumulative values over time or across different categories.