[Koha] Looking for help with a report

Is there someone who can provide the SQL for me for a report that simply lists the itemnumber, barcode, and itemcallnumber for all items of a given Item Type. I'd like the report to prompt (with a pull-down) the list of all Item Types I have so that I can select it to report on. I think this should be easy but for some reason I can't get the pull-down list to populate with anything at all. THANKS! Steve