Adding summary statistics

One of the advantages of creating a grouped DataWindow object is that you can have PowerBuilder calculate statistics for each group. To do that, you place computed fields that reference the group. Typically, you place these computed fields in the group's trailer band.

To add a summary statistic:

Select Insert>Control>Computed Field from the menu bar.
Click in the Design view where you want the statistic.

The Modify Expression dialog box displays.
Specify the expression that defines the computed field (see below).
Click OK.

A shortcut to sum values If you want to sum a numeric column, select the column in Design view and click the Sum button in the Controls drop-down toolbar. PowerBuilder automatically places a computed field in the appropriate band.

Specifying the expression

Typically, you use aggregate and other functions in your summary statistic. PowerBuilder lists functions you can use in the Functions box in the Modify Expression dialog box. When you are defining a computed field in a group header or trailer band, PowerBuilder automatically lists forms of the functions that reference the group:

The sample shows the scrollable Functions box in the expression dialog box. Displayed are available functions in alphabetical order.

You can paste these templates into the expression, then replace the #x that is pasted in as the function argument with the appropriate column or expression.

For example, to count the employees in each department (group 1), specify this expression in the group trailer band:

Count( Emp_Id for group 1 )

To get the average salary of employees in a department, specify:

Avg( Salary for group 1 )

To get the total salary of employees in a department, specify:

Sum( Salary for group 1 )

The sample shows the group trailer band with the words Average Salary: and the partially visible expression a v g ( salary for group 1 ). Also in the group trailer band are the words Total Salary: and the partially visible expression sum ( salary for group 1 ).

At runtime, you see this:

The sample shows the group header band at top. It includes labels for the four rightmost columns Emp I D, Emp F Name, Emp L name, and Salary. Below it at left is the header Dept I d and below that is the I D 500. On the next line start the rows of data for the department. At bottom right are the words Average Salary: and a dollar amount, then the words Total Salary: and a dollar amount.