How to pass multiple values to a multivalued parameter in SSRS

Question

I will try to explain the issue as best as I can by oversimplifying the report structure. Report one contains 1 group called ResourceCenter and then one line of totals under it. The totals are actually a group but the grouping is done in SQL and are presented in a detail group. The report looks something like this:

Report 1

ResourceCenter 1
Total1 11 
Total2 4
Total3 8

ResourceCenter2
Total1 12
Total2 11
Total3 6

From this report, I need to drill through to another report that has a bunch of multi-valued parameters. For the drillthrough, I am able to use single values for everything except for EmployeeNumber. For that, I need to be able to pass a list of EmployeeNumbers to the multi-valued parameter in Report 2. The EmployeeNumbers are not currently present in any DataSet or parameter in Report 1 but are based on ResourceCenter. So, if the user has run Report 1 and clicks on ResourceCenter 1, I need to be able to pass a list of EmployeeNumbers associated with ResourceCenter 1 to the multi-valued parameter in Report 2 in a way that Report 2 will handle it correctly.

NOTE: I should add that I have created two SQL functions that accept an input of ResourceCenter and then return a list of employees. One is a table-valued function that returns a single column of EmployeeNumbers. The other is a scalar-valued function that returns the EmployeeNumbers as comma-separated values. I then have some custom code that runs the SQL function in the background and returns the list. I have not had any success with returning a dataset that SSRS can use but I have been able to get the scalar-valued function to 'work' in the sense that I can create a field on a dummy report and see the output. I have not had any luck getting Report 2 to accept a comma-separated list, though.

Answer 1

This person was doing a drill-through and appears to have solved a similar problem with a multi-value parameter. In that case it had to be formatted for an IN clause.

=SPLIT(JOIN(Parameters!SomeParameterName.Value,","),",")

If Report2 won't take it in this format, you might have to add a separate single-valued parameter that will accept a comma-separated string, which you then have to parse.