Few days back I was debugging SAP standard function module in HR module of ECC. When I finished what I wanted to see in the debugger I let it run till the end. The FM was not progressing so I turned to TA SM50 to see whether it is doing something. Suddenly I saw that my process is running but what got my attention was Table column indicating that table is unknown (Tunknown). It took few more seconds and the FM and work process finished correctly and entry in the SM50 disappeared. I didn't pay attention anymore to that but I just tweeted about it.
My twitter friend Ram Manohar Tiwari however after some conversation pointed me to SAP Note 1524630 which discuss this issue in detail. Actually while using ADBC (ABAP Database Connectivity) API for Native SQL interface it can lead to situation in which system can’t really determine what table is actually used. In my case usage of ADBC is indicated by class CL_SQL_STATEMENT which is ADBC related.
As the notes suggests there always will be Tunknown entries in the SM50 as there are cases where “guessing” of used tables by DbSl interface (database SQL library) doesn't help.