Defining a computed field in the DataWindow painter Design
view
To define a computed field in the DataWindow painter Design
view
-
Select Insert>Control>Computed Field from the menu
bar. -
Click where you want to place the computed field.
If the calculation is to be based on column data that
changes for each row, make sure you place the computed field in
the detail band.The Modify Expression dialog box displays, listing:
-
DataWindow expression functions you can use in the
computed field -
The columns in the DataWindow object
-
Operators and parentheses
-
-
Enter the expression that defines the computed field as
described in Entering the
expression. -
(Optional) Click Verify to test the expression.
PowerBuilder analyzes the expression.
-
Click OK.
Entering the
expression
You can enter any valid DataWindow expression when defining a
computed field. You can paste operators, columns, and DataWindow
expression functions into the expression from information in the
Modify Expression dialog box. Use the + operator to concatenate
strings.
You can use any built-in or user-defined global function in an
expression. You cannot use object-level functions.
DataWindow expressions
You are entering a DataWindow expression, not a SQL
expression processed by the DBMS, so the expression follows the
rules for DataWindow expressions. For complete information about
DataWindow expressions, see DataWindow Expression Functions in DataWindow Reference.
Referring to next and previous
rows
You can refer to other rows in a computed field. This is
particularly useful in N-Up DataWindow objects when you want to
refer to another row in the detail band. Use this syntax:
|
1 |
ColumnName[x] |
where x is an integer. 0 refers to the current row (or first
row in the detail band), 1 refers to the next row, –1 refers to the
previous row, and so on.
Examples
The following table shows some examples of computed
fields.
|
To display |
Enter this expression |
In this band |
|---|---|---|
|
Current date at top of each page |
Today() |
Header |
|
Current time at top of each page |
Now() |
Header |
|
Current page at bottom of each |
Page() |
Footer |
|
Total page count at bottom of each |
PageCount() |
Footer |
|
Concatenation of Fname and Lname columns for |
Fname + ” ” + Lname |
Detail |
|
Monthly salary if Salary column contains annual |
Salary / 12 |
Detail |
|
Four asterisks if the value of the Salary |
IF(Salary> 50000, “****”, “”) |
Detail |
|
Average salary of all retrieved |
Avg(Salary) |
Summary |
|
Count of retrieved rows, assuming each row |
Count(EmpID) |
Summary |
For complete information about the functions you can use in
computed fields in the DataWindow painter, see DataWindow Reference.
Menu options and buttons for common
functions
PowerBuilder provides a quick way to create computed fields
that summarize values in the detail band, display the current date,
or show the current page number.
To summarize values
-
Select one or more columns in the DataWindow object’s
detail band. -
Select one of the options at the bottom of the cascading
menu: Average, Count, or Sum.The same options are available at the bottom of the
Controls drop-down toolbar on the PainterBar.PowerBuilder places a computed field in the summary band
or in the group trailer band if the DataWindow object is
grouped. The band is resized automatically to hold the computed
field. If there is already a computed field that matches the one
being generated, it is skipped.
To insert a computed field for the current date or page
number
-
Select Insert>Control from the menu bar.
-
Select Today() or Page n of n from the options at the
bottom of the cascading menu.The same options are available at the bottom of the
Controls drop-down toolbar on the PainterBar. -
Click anywhere in the DataWindow object.
If you selected Today, PowerBuilder inserts a computed
field containing this expression: Today(). For Page n of n, the
computed field contains this expression: ‘Page ‘ + page() + ‘ of
‘ + pageCount().
Adding custom buttons that place
computed fields
You can add buttons to the PainterBar in the DataWindow
painter that place computed fields using any of the aggregate
functions, such as Max, Min, and Median.
To customize the PainterBar with custom buttons for placing
computed fields
-
Place the mouse pointer over the PainterBar and select
Customize from the pop-up menu.The Customize dialog box displays.
-
Click Custom in the Select palette group to display the
set of custom buttons. -
Drag a custom button into the Current toolbar group and
release it.The Toolbar Item Command dialog box displays.
-
Click the Function button.
The Function For Toolbar dialog box displays.
-
Select a function and click OK.
You return to the Toolbar Item Command dialog box.
-
Specify text and microhelp that displays for the button,
and click OK.PowerBuilder places the new button in the PainterBar. You
can click it to add a computed field to your DataWindow object
the same way you use the built-in Sum button.