Video tutorial on using subreports in Jaspersoft's iReport Designer.
A subreport is a section of a report that is based a a different query. Subreports are linked to reports by parameters and a subreport may contain subreports itself.
This example shows a report that issues 3 queries to each of 3 tables using subreports. While a single query joining the 3 tables can create the same report using iReport's grouping capabilities, the subreport offers the following advantages:
1. Subreports can use datasources different than the parent report,
2. It may be easier to write individual queries, and
3. Subreports may be reused among reports.