Frequently, the data in a subreport supplements the data in the primary report. You might, for example, have customer data in a primary report and then use subreports to show the orders for each customer.
In such cases, you will need to coordinate the data in the primary report with the data in the subreport so that the orders in each subreport match up with the correct customer.
To do this, you need to specify a field that is common to both the subreport and the primary report. With the Subreport Links dialog box, you create a link between the two common fields. Crystal Reports uses the link to match up records from the primary report to those in the subreport. The link makes certain that the "orders" data in the subreport sits on the same row as the corresponding "customer" data in the primary report.