Tableau Functions Unveiled: SUM vs. WINDOW_SUM with Practical Examples

 Let's explore the difference between the SUM and WINDOW_SUM functions in Tableau with examples. This will serve as a tutorial to illustrate their distinctions.

Example Data: We'll use a sample dataset with columns for Date and Sales. The dataset represents daily sales data over a period.

Tutorial: Comparing SUM and WINDOW_SUM Functions in Tableau

Step 1: Open Tableau and Connect to Your Data

Launch Tableau and connect to your dataset (e.g., Excel, CSV, database).

Step 2: Create a Simple Visualization Using SUM

Drag the Date dimension to Columns and the Sales measure to Rows to create a line chart showing daily sales over time.

This chart displays the total sales for each day using the SUM aggregation.

Step 3: Create a WINDOW_SUM Calculation

Right-click anywhere on a blank area in the calculated field pane and select "Create Calculated Field."

To create a WINDOW_SUM calculation, use the following syntax:

WINDOW_SUM(SUM([Sales]))

This calculation tells Tableau to calculate the running sum of the Sales measure.

Step 4: Use the WINDOW_SUM Calculation in a Visualization

Drag the WINDOW_SUM calculation you created (e.g., WINDOW_SUM(SUM([Sales]))) to the Rows shelf alongside the Date dimension.

This will create a new line chart that displays the running sum of sales over time.

Step 5: Customize Your Visualization

Customize the visualization as needed by adding labels, colors, or other dimensions to enhance the presentation of the data.

Step 6: Understand the Difference

Now, let's compare the two visualizations:

The chart using SUM shows the daily total sales, providing insights into the sales for each individual day.

The chart using WINDOW_SUM shows the running total of sales. In this chart, each data point represents the cumulative sales up to that point in time. For example, if you see a point at $10,000 on a certain date, it means that the cumulative total sales up to that date is $10,000.

Step 7: Adjust the Calculation Window

By default, the WINDOW_SUM function calculates the running sum over all rows. If you want to specify a different window or range of rows, you can modify the calculation. For instance, to calculate the running sum of the last 7 days of sales, you can use the following calculation:

WINDOW_SUM(SUM([Sales]), -6, 0)

In this calculation, -6 represents the start of the window (6 rows before the current row), and 0 represents the end of the window (the current row).

Step 8: Save and Share Your Workbook

Once you're satisfied with your visualizations, save your Tableau workbook and share it with others as needed.

In summary, the SUM function provides the total aggregation of a measure for each data point, while the WINDOW_SUM function calculates the running or cumulative total of that measure up to each data point. These functions serve different analytical purposes and can be used based on the specific insights you want to gain from your data.