Calculating Running Totals in SQL Server: A Step-by-Step Guide

Calculating Running Totals in SQL Server

Understanding the Problem and Query Issues

As a developer, have you ever encountered a situation where you need to calculate running totals or cumulative sums for a specific date range? In this article, we’ll explore how to achieve this using SQL Server’s window functions.

The provided Stack Overflow question illustrates the problem: calculating a running total in SQL Server by date. The user is trying to find the cumulative sum of volume from October 1st, 2018, but keeps getting incorrect results.

Let’s break down the query issues and explore the correct solution using window functions.

Query Issues

The original queries use an INNER JOIN to join the VOLUME table with itself, comparing each date to all subsequent dates. This approach is incorrect because it doesn’t account for the actual running total.

The first query:

SELECT [Month/Year], [Date], SUM([Volume]) as 'sum' 
FROM VOLUME 
WHERE [Month/Year] = '2018-10-01' 
GROUP BY [Month/Year], [Date] 
ORDER BY [Date]

This query groups the data by date and calculates the sum of volume for each group. However, it doesn’t take into account the running total from previous dates.

The second query:

SELECT a.[date], SUM(b.[Volume]) as barge_sum 
FROM VOLUME a 
INNER JOIN VOLUME b ON a.[date] > b.[date] 
WHERE a.[Month/Year] = '2018-10-01' 
GROUP BY a.[date] 
ORDER BY a.[date]

This query uses an INNER JOIN to compare each date to all subsequent dates. However, it doesn’t correctly calculate the running total.

Correct Solution

The correct solution uses window functions, specifically the SUM() function with an OVER clause. The OVER clause allows us to specify the window over which the function is applied.

Here’s the corrected query:

SELECT [Month/Year], [Date], SUM([Volume]) OVER (ORDER BY [Date]) as barge_sum 
FROM VOLUME 
WHERE [Month/Year] = '2018-10-01'

In this query:

We select the [Month/Year] column and the [Date] column.
We use SUM() to calculate the running total of volume for each date.
The OVER (ORDER BY [Date]) clause specifies that we want to apply the sum function over the [Date] column, in ascending order.

This query correctly calculates the running total by date.

Running Total with Grouping

If you need to group the data by a specific column (e.g., [Month/Year]) and calculate the running total for each group, you can modify the query as follows:

SELECT [Month/Year], [Date], SUM([Volume]) OVER (PARTITION BY [Month/Year] ORDER BY [Date]) as barge_sum 
FROM VOLUME 
WHERE [Month/Year] = '2018-10-01'

In this modified query:

We use PARTITION BY [Month/Year] to group the data by [Month/Year].
The rest of the query remains the same, using SUM() with an OVER (ORDER BY [Date]) clause to calculate the running total for each group.

Running Total without Grouping

If you don’t need to group the data and simply want to calculate the running total for a specific date range, you can use the following query:

SELECT [Month/Year], [Date], SUM([Volume]) OVER (ORDER BY [Date] ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as barge_sum 
FROM VOLUME 
WHERE [Month/Year] >= '2018-10-01' AND [Month/Year] < '2019-01-01'

In this query:

We use ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW to specify the window over which the sum function is applied.
The ROWS clause includes all rows from the earliest date in the range (UNBOUNDED PRECEDING) up to and including the current row.

This query calculates the running total for the specified date range without grouping the data.

Conclusion

Calculating running totals in SQL Server can be achieved using window functions, specifically SUM() with an OVER clause. By specifying the correct window over which the function is applied, you can accurately calculate cumulative sums for specific date ranges or grouped data.

Remember to carefully examine your query and consider the requirements of your use case when choosing between different window function options.

Last modified on 2025-03-26