By default, Power BI assigns a default summarization to numeric columns, and this default summarization is usually a sum operation. Columns that have been assigned a default summarization are denoted by Power BI with a Sigma symbol (∑). DateKey, Day Number of Week, Day Number of Month, Day Number of Year, and Week Number of Year have all been assigned a default summarization by Power BI in the following screenshot:

Figure 23-Default assigned columns for summarization

This automatic assignment of default summarizations can cause a lot of confusion to report developers in Power BI. Columns that have a default summarization assigned will be automatically aggregated with their assigned default summarization when added to a report. The columns identified in Figure 23 are generally descriptive attributes that help to explain the data; these columns would rarely be aggregated. Take a look at the following screenshot:

Figure 24-Year column from date table

In Figure 24, the Year column from the date table has been added into a table visual, and the expected behavior is to see a distinct list of years (2005, 2006, 2007, 2008, 2009, and 2010). Instead, a value of 4,398,433 is returned. Instead of returning a distinct list, the report returns a sum of all records from the year column in the date table. See the screenshot and steps shown next to adjust the default summarization:

Figure 25-Adjust the default summarization

The preceding screenshot walks through changing the default summarization, with detailed steps listed here:

Select the report view from the left navigation bar.
Expand the date table and select Calendar Quarter, highlighted by a yellow box.
Select the modeling ribbon.
Click the dropdown for Default Summarization, and select Don't summarize.

Repeat the above process for each column in the date table that has been assigned a default summarization by Power BI.