Imagine that you have a report that contains contact information about your customers and that information is grouped by region. You decide that you want to include information for your suppliers in each region as well, on the same report. But the supplier data is located in a data file that cannot be linked to the main database table that contains all your customer information.
You can use a sub report to overcome this problem of non-linkable data. The two tables contain matching values in the fields, but the fields themselves cannot be linked due to different field names using-the Visual Linking Expert. Because the supplier data file cannot be linked to the customer table, you must create two separate reports. Insert one report into the other as a sub report. When a reader looks at the report, he will have no idea that one is the main report and one if the sub report.
Use sub reports to overcome other database shortcomings, as well. For example, if you have two tables linked for a report but the second table is not indexed, looking up values in that table may take a long time if SCR has to do the work. If, instead, you design a sub report with effective selection criteria, the database’ server does the selection instead of SCR, which speeds up the report processing time.