Crystal Reports 10: The Complete Reference

Probably the most common use for a parameter field is in report record selection. By creating a parameter field and using it with the Select Expert or a record-selection formula, you can prompt the viewer to provide variable information when the report runs, and have the report record selection reflect the viewer s choices.

After creating the desired parameter fields, use the toolbar button or pull-down menu option to display the Select Expert. Add a selection tab for the database field you want to compare to the value the viewer enters into the parameter field. In the operation drop-down list, choose the appropriate operation for the parameter action you need, such as is equal to for a region selection parameter, greater than for an order threshold parameter, or is like for a string-matching name parameter. Keep in mind that you may need to use a different Select Expert operation with parameter fields than you would otherwise . You ll typically use is equal to even if you want to allow multiple values or range values to be supplied by a parameter (not is between or is one of ). When you choose the drop-down list to see sample database values, you ll see parameter fields of the same data type in the list. Choose the correct parameter field.

If you use the Formula Editor to edit the record-selection formula, you ll see all parameter fields (regardless of data type) in the Field Tree box. Choose the parameter field you want to use in the record-selection formula. The formula may look something like this:

{Customer.Region} = {?Region}

Make sure you choose a parameter field of the same data type, or use functions to convert the parameter field to the correct data type. If you try, for example, to compare a numeric parameter field to a string database field, you ll receive an error in the Formula Editor.