Defining the expression – PB Docs 2019

A validation rule is a boolean expression. PowerBuilder
applies the boolean expression to an entered value. If the
expression returns “true”, the value is accepted. Otherwise, the
value is not accepted and an ItemError event is triggered.

What expressions can
contain

You can use any valid DataWindow expression in validation
rules.

Validation rules can include most DataWindow expression
functions. A DataWindow object that will be used in PowerBuilder can
also include user-defined functions. DataWindow expression functions
are displayed in the Functions list and can be pasted into the
definition.

For information about these functions, see DataWindow Expression Functions in DataWindow Reference.

Use the notation @placeholder (where placeholder is any group
of characters) to indicate the current column in the rule. When you
define a validation rule in the Database painter, PowerBuilder
stores it in the extended attribute system tables with the
placeholder name. At runtime, PowerBuilder substitutes the value of
the column for placeholder.

Pasting the
placeholder

The @col can be easily used as the placeholder. A button in
the Paste area is labeled with @col. You can click the button to
paste the @col into the validation rule.

An example

For example, to make sure that both Age and Salary are greater
than zero using a single validation rule, define the validation rule
as follows:

Then associate the validation rule with both the Age and
Salary columns. At runtime, PowerBuilder substitutes the appropriate
values for the column data when the rule is applied.