Microsoft SQL Server 2012 Reporting Services

Chapter 33. Programming report design components

As part of the report development phase of the reporting life cycle, you use expressions to calculate a value that displays in your report or to change a property value that affects the behavior or appearance of a report item, as described in Chapter 11. When you need to use the same complex expression many times in the same report, you might find it easier to write one custom function that you can use as many times as you need throughout the report. Then you have only one place in the report to update the expression if the report requirements change later. Another advantage of using custom functions is the ability to use more advanced logic in your expressions, such as loops that use FOR or WHILE ...