Hi,

For having a calculated column, you have basically 2 options:

• Create a calculated column at the SharePoint list level. You can then retrive this calculated column like any other SharePoint column.
• Create a calculated column at the Reporting Services level. This is a pure Reporting Services feature that is not specific to Enesys RS Data Extension. Please see the following links for more information : 
  http://msdn2.microsoft.com/en-us/library/ms156295.aspx
  http://codebetter.com/blogs/peter.van.ooijen/archive/2005/07/08/128947.aspx

Though there are several option, to make it simple, i would recommend sorting at the report level. Please see the following link: http://technet.microsoft.com/en-us/library/ms170712.aspx.

To limit the number of rows once it has been sorted as you, you may use the RowNumber() expression with reporting services. Once you are there, I could help you further.

I would recommend that you get some experience on using Reporting Services report designer. Many documentation and tutorial are available.

Please note that we will probably include a SQL Engine into Enesys RS Data Extension next major version so that those kind of manipulation will be easily be done at the query level without necessarily relying on Reporting Services features.

Regards,