It is always good to enrich SSRS reports with multi-value parameters; users have more flexibility to combine different reporting scenario with no need to run a report for different parameter values separately. On the other hand, developers can craft their skills to embed multi-value parameters into report datasets; referencing different rows, labels and values from those parameters into some custom controls within reports is another competence which can also be quickly obtained.

Alright, report is developed and deployed for users. They requested to create report subscriptions and now enjoy luxury of scheduled results delivery in different formats. Report Manager in Native mode and SharePoint in SSRS Integrated mode read report parameters metadata pretty well and allow setting new values for multi-value parameters or keep default settings.

However when you’re dealing with data-driven subscription, it’s not that easy to pass data query values for multi-value parameters. You have a choice:
1) To be happy with reports default values and change nothing in report subscription 
2) You can still be happy and create regular subscription with manually setting parameter values
3) You can programmatically define parameter values using CreateDataDrivenSubscription method of the ReportingService assembly
4) Also, you can be crazy enough and built set of XML parameters tags in Parameters column and update the dbo.Subscriptions table of your Report Server instance.

But still, it doesn't let to link a data element from data-driven subscription query with your multi-value parameter; how would you pass several values in one columns of a single record. And I think you’ve already guessed one of the right answers: delimited string of values!

Here is how I’ve made it working for a project, where my client wanted to trigger report subscriptions from their web UI and each SSRS report executions could have different multi-value parameters values.

1) I've created two multi-value parameters in my SSRS reports:

        b. ReportParameterActual; kept it Visible, Available Value – Query from a dataset, Default values – Specify values with the following expression:
=Split(@ReportParameter, ",")
2) Once this report was deployed, I’ve created a data driven subscription where my data query looked similar to this: select ReportParameter = ‘Value1,Value2,Value3’ from MyTable
3) And then I mapped ReportParameter from the report with the ReportParameter column from this query.

This was the whole solution to the problem. ReportParameterActual was visible parameter for users and they could interact and set different values themselves beyond the subscriptions definition. ReportParameter was the actual interface and gateway for default values (which with data-driven subscription now became a dynamic control on set of values that would be supplied to multi-value ReportParameter (i.e. ReportParameterActual) in different subscription scenarios). And Split(@ReportParameter, ",") was the whole trick 🙂

Update (2014-09-03): Richard D'Angelo asked me to share the RDL with the solution. I couldn't upload the actual client report, but I've made a sample one based on the [AdventureWorksDW2014].[dbo].[DimGeography] table. You can get this sample through this link - MultiValueParameterReport.rdl.

Happy data adventures!