On-demand sub reports Nave as their name implies—users call (hem up on demand, rather than having them appear automatically. You can designate a sub report to be an on-demand sub report when you add the sub report to the main report, or you can format the sub report after it has been inserted to be an on-demand sub report,
The on-demand feature of sub reports allows you to process and preview the report without the sub report data being retrieved from your database or printing on your report. This way, viewers of the report can request the sub report data only if they need or want to.
On-demand sub reports can be useful when inserting a sub report for each group (at any group level). Some viewers of the report may not need the sub report data because they do not need that much detail or extra information. On the other hand user of the same report may want to see the sub reports.
The report and sub report just linked in the previous section will serve as a good. , example here. You have a sub report that prints in each Group Footer, providing information on the top five products ordered by each customer, Readers of the report may not need to see this information for every customer, but may want the ability to click a link to sec that information if and when they want. Formatting the sub report to be on-demand provides this functionality.