One of the key features of any report is the ability to display summary, or aggregate, information. For example, a sales report can show the overall sales total; sales subtotals by product type, region, or sales representatives; average sales figures; or the highest and lowest sales figures.
Aggregating data involves performing a calculation on a set of values rather than on a single value. For a simple listing report, aggregate calculations are performed on values in a specific field, over all the data rows in the report. The listing report in Figure 12-1 displays aggregate data at the end of the report.
Figure 12-1. A simple listing report that displays detail and aggregate data
In the example, BIRT calculates ...