First of all, As you are already using prepared statements ... Then I'd suggest using placeholders which requires changing `filter_id` = $set to `filter_id` = ? then you can supply the value of filter_id to the execute method

You don't actually need to call your subroutine with the '&' the, use it only if you want to get the value of @_

Finally, I don't think you have any problem with your code and it should be assigning the value correctly.