Inserting aggregate functions
Inserting Aggregate Function
So far we have manually inserted the aggregate functions into “Text” objects. Now we will look at other ways to insert aggregate functions.
First we can use the “System text” object to output an aggregate. In fact this object is similar to a “Text” object with its own special editor for more easily specifying system variables or aggregate functions:

Select an aggregate function, then the data band over which the aggregate is to be calculated), a DataSet, which is usually the same as a DataSet property of the selected band, and finally a DataField or an expression whose value is to be calculated. You can also set the “Count invisible bands” and “Running totals” flags, if required.
The second method is to use a “Text” object and click the
button in its editor: this opens a dialogue similar to the “System text” object editor. When the OK button is clicked a call to the aggregate function is inserted into the object's text.
Inserting Datafield
In the same way you can insert datafield. You just set DataSet and DataField properties:

Inserting Other Data
In this form you can also select system variables, but not all are available. It's easier to drag from the Data tree and drop onto workspace.
If you want to write an expression or text or more expressions in one object, select Text and write in any text in the input field. In this case you did not acquire anything with a special object, as this is exactly the same as writing to "Text" object.