In our recent project, I’ve got a request to let custom reports to support multiple values in parameters. It seemed to be a little effort but I spent many hours to make it works.
Many recommendations advice to join the parameter’s multiple values in one using a function JOIN in SQL Reporting Services:
Then using Transact-SQL IN statement check if the variable of the SQL query is among the selected values.
Unfortunately, 'as is' it didn’t work for me.