A subreport is a report within a report
In Crystal Reports, there are two types of subreports — unlinked and linked.

The Unlinked Subreport
Unlinked subreports do not attempt to coordinate their data with the primary report. In other words, an unlinked subreport does not match up records to the records within a primary report. Unlinked subreports do not need to use the same data as the primary report — in fact, an unlinked subreport often does not even share the same data source as the primary report.

The Linked Subreport
Linked subreports, in comparison to unlinked subreports, do share the same data source as a primary report. A linked subreport's data is linked and coordinated with the primary report's data. In other words, both reports contain records that are matched up.

As an example, say that your primary report contains employee information and your subreport contains order information (where this order information is linked to the employee information). For each employee record, a linked subreport would include all orders for that employee only. You can try your hand at creating a linked subreport later in this chapter.