Using DataWindow expression functions – PB Docs 126

Using DataWindow expression functions

In the DataWindow painter, you can use DataWindow expression functions
in expressions for computed fields, filters, validation rules, and graphed
data, with some exceptions.

The dialog boxes in which you define expressions include a
list box that lists the available functions and their arguments.
The dialog boxes make it easy to insert a function into the expression.

For information about expressions, see Chapter 1, “DataWindow Operators
and Expressions.”

Return values for functions and
expressions

DataWindow expression functions can return the following datatypes:

  • Double

  • Decimal

  • String

  • DateTime

  • Time

Within an expression, a function can return other datatypes
(such as boolean, date, or integer), but the final value of an expression
is converted to one of these datatypes.

Restrictions for aggregate functions

An aggregate function is a function (such as Avg, Max, StDev,
and Sum) that operates on a range of values in
a column. When you use an aggregate function, some restrictions
apply. You cannot use an aggregate function:

  • In a filter

  • In a validation rule

  • As an argument for another aggregate function

When you use aggregate functions, they cancel the effect of
setting Retrieve Rows As Needed. To do the aggregation, the DataWindow object always retrieves
all rows.

User-defined functions in PowerBuilder

You can include user-defined functions in DataWindow expressions.
The datatype of the function’s return value can be any
of the following: double, decimal, string, boolean, date, DateTime,
or time. The function must be defined as a global function so that
it is available to the DataWindow object. However, a global function
argument of datatype boolean cannot be provided by a DataWindow
expression because it does not map to any of the datatypes listed
in “Return values for functions and
expressions”
.

Built-in DataWindow expression functions cannot be overridden.
For example, if you create a global function called Today,
it is used instead of the PowerScript system function Today,
but it is not used instead of the DataWindow
expression function Today.

Formatting for the locally correct display of
numbers

No matter what country you are creating objects and developing
an application in, you must use U.S. number notation in numbers
or number masks in display formats, edit masks, and DataWindow expressions.
This means that when you specify a number or number mask, use a
comma as the thousands delimiter and period for the decimal place.

Numbers display appropriately in whatever countries you deploy
applications in. At runtime, the locally correct symbols for numbers
display (because the international Control Panel settings are used)
when numbers are interpreted. For example, in countries where comma
represents the decimal place and period represents thousands, users
see numbers in those formats at runtime.

For information about the locally correct
display of dates and day names, see String and DayName.


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