Filtering rows
You can use WHERE and HAVING clauses
and retrieval arguments in the SQL SELECT statement
for the DataWindow object to limit the data that is retrieved from the
database. This reduces retrieval time and space requirements at
runtime.
However, you may want to further limit the data that displays
in the DataWindow object. For example, you might want to:
-
Retrieve many rows and initially
display only a subset (perhaps allowing the user to specify a different
subset of rows to display at runtime) -
Limit the data that is displayed using DataWindow expression functions
(such as If) that are not valid in the SELECT statement
Using filters
In the DataWindow painter, you can define filters to limit the rows
that display at runtime. Filters can use most DataWindow expression functions or user-defined
functions.
Filters do not affect which rows are retrieved
A filter operates against the retrieved data. It does not
re-execute the SELECT statement.
Defining a filter
To define a filter:
-
In the DataWindow painter, select Rows>Filter
from the menu bar.The Specify Filter dialog box displays:
-
In the Specify Filter dialog box, enter a boolean
expression that PowerBuilder will test against each retrieved row.If the expression evaluates to true, the
row is displayed. You can specify any valid expression in a filter. Filters
can use any non-object-level PowerScript function, including user-defined
functions. You can paste commonly used functions, names of columns,
computed fields, retrieval arguments, and operators into the filter. International considerations
The formatting that you enter for numbers and currency in
filter expressions display the same way in any country. Changing
the regional settings of the operating system does not modify the
formatting displayed for numbers and currency at runtime.For information about expressions for filters,
see the DataWindow Reference. -
(Optional) Click Verify to make sure the expression
is valid. -
Click OK.
Only rows meeting the filter criteria are displayed in the
Preview view. Filtered rows and updates
Modifications of filtered rows are applied to the database
when you issue an update request.
Removing a filter
To remove a filter:
-
Select Rows>Filter from the menu
bar. -
Delete the filter expression from the Specify
Filter dialog box, then click OK.
Examples of filters
Assume that a DataWindow object retrieves employee rows and three
of the columns are Salary, Status,
and Emp_Lname. Table 23-1 shows some examples of
filters you might use.
|
To display |
Use this filter |
|---|---|
|
Employees with salaries over $50,000 |
|
|
Active employees |
|
|
Active employees with salaries over $50,000 |
|
|
Employees whose last names begin with |
|
Setting filters dynamically
You can use the SetFilter and Filter methods
in a script to dynamically modify a filter that was set in the DataWindow painter.
For information about SetFilter and Filter,
see the online help.