Use the Categories window to select which data to use on the report. The left pane shows the data categories you can access. To see the fields in a category, select it and click the View Category Fields icon.

Click on the below links for details:

Data Categories are tables of data, which are organized by rows and columns. Columns are also known as data fields. A row of data has entries for one or more columns in the category. When you add a data field onto a report you are seeing the information in one column of data for every row in the category.

For example, a data category for Employees could have columns for the first and last names of each employee, an identification number, and a home phone number. Each row represents a person, and each column contains a specific type of information such as last name or phone number.

You can add entire category at a time to a report, but in the report view you select columns from the selected category that you want to see. When you add a data field to the report design, even though you only see one column, the rest of the table is still present behind the scenes. You will never lose the connections between items in each row, and you can always add more fields.

Note: You can add only one category to a report at a time, however you can remove and re-select category if required, but doing so you will loose any fields already placed on report designed from the old category.

If you find that your report has unexpected duplicate values or empty rows, the cause is most likely that you your category includes column that allows to have repetitive values as it is not the primary parameter of that category, but important in generating various statistics.

For example, a report has category Orderdetails. Orderdetails will have unique value for each order placed, however will have duplicating value for Employee name, as same employee may be creating the orders. So when report need to be generated not based on order ID and need to be grouped on Employee Name, we can suppress the repeating values displayed on the report for better visibility.

There are several ways to eliminate these duplicates. You can suppress duplicates for the Employees name, which will show blank rows for consecutive duplicates. In order to do that, select the suppress duplicates check box for the Employee Name Field.

You can also suppress entire row for the duplicating value. Select the cell and click the Suppress Duplicates icon. In such case only one record per employee name will be displayed, and rest of them will be discarded. This can be used to extract unique values on column, and record relevant to it.