SSRS multi-value parameter using a stored procedure

You need three things:

1. In the SSRS dataset properties, pass the multi-value param to the stored procedure as a comma-delimited string

   =Join(Parameters!TerritoryMulti.Value, ",")
   

2. In Sql Server, you need a table-value function that can split a comma-delimited string back out into a mini table (eg see here). edit: Since SQL Server 2016 you can use the built-in function STRING_SPLIT for this

3. In the stored procedure, have a where clause something like this:

   WHERE sometable.TerritoryID in (select Item from dbo.ufnSplit(@TerritoryMulti,','))
   

   … where ufnSplit is your splitting function from step 2.

(Full steps and code in my blog post ‘SSRS multi-value parameters with less fail’):