## Chapter 9 Aggregating Data

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 over a set of data rows. For a simple listing report, the aggregate calculations are performed over all the data rows in the report.

BIRT calculates an average payment in a report by adding the payment amounts in every row, then dividing the total by the number of rows.